Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation Our consolidated financial statements include our accounts and those of our majority-owned and controlled subsidiaries after elimination of intercompany accounts and transactions. Equity investments over which we are able to exercise significant influence but do not control the investee are accounted for using the equity method. We determine whether we have a controlling financial interest in an entity by first evaluating whether the entity is a voting interest entity or a variable interest entity, or VIE. Voting interest entities are entities that have sufficient equity and provide equity investor voting rights that give them power to make significant decisions relating to the entity’s operations. The usual condition for a controlling financial interest in a voting interest entity is ownership of a majority voting interest. In VIEs, a controlling financial interest is attained through means other than voting rights and the entities lack one or more of the characteristics of a voting entity. We have unconsolidated equity investments in third-party businesses. Equity investments with readily determinable fair values are recorded at fair value. Equity investments without readily determinable fair values are recorded using the measurement alternative. Under the alternative, we measure investments without readily determinable fair values at cost, less impairment, adjusted for observable price changes from orderly transactions for identical or similar investments. We make a separate election to use the measurement alternative for each eligible investment, and reassess whether an investment qualifies for the alternative at each reporting period. Adjustments resulting from impairment, fair value, or observable price changes are recorded in other income, net in our consolidated statements of operations.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Our estimates, judgments and assumptions are continually evaluated based on available information and experience. Because of the use of estimates inherent in the financial reporting process, actual results could differ from those estimates. Estimates are used when accounting for revenue recognition, allowances for doubtful accounts, allowance for hardware returns, estimates of obsolete inventory, long-term incentive compensation, stock-based compensation, income taxes, legal reserves, contingent consideration and goodwill and intangible assets.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid instruments purchased with an original maturity from the date of purchase of three months or less to be cash equivalents.
Accounts Receivable and Notes Receivable	Accounts Receivable Accounts receivable are principally derived from sales to customers located in the United States and Canada. Substantially all of our sales in Canada are transacted in U.S. dollars. Revenue in countries outside of North America accounted for 2%, 1% and less than 1% of our total revenue for the years ended December 31, 2018, 2017 and 2016, respectively. Accounts receivable balances related to service providers partners outside of North America were 4% as of December 31, 2018 and 2017. Our accounts receivable are stated at estimated realizable value. We utilize the allowance method to provide for doubtful accounts based on management’s evaluation of the collectibility of the amounts due. Our estimate is based on historical collection experience and a review of the current status of accounts receivable. Each of our service provider partners is evaluated for creditworthiness through a credit review process at the inception of the arrangement or if risk indicators arise during our arrangement at such other time. Our terms for hardware sales to our service provider partners and distributors typically allow for returns for up to one year. We apply our estimate as a percentage of sales monthly, based on historical data, as a reserve against revenue to account for our provision for returns. We have not experienced write-offs for uncollectible accounts or sales returns that have differed significantly from our estimates. Notes Receivable Notes receivable are presented net of an allowance for uncollectibility, if any. We accrue interest on notes receivable based on the contractual terms of the note. Outstanding notes receivable that are aged 30 days or more from the contractual payment date are considered past due. Notes receivable are evaluated for impairment at least quarterly. Impairment occurs when it is deemed probable that we will not be able to collect all amounts due according to the contractual terms of the loan. Factors considered in determining impairment include payment status, collateral value and the probability of collecting payments when due. We do not accrue interest on notes receivable that are considered impaired or are greater than 90 days past due based on their contractual payment terms. Notes receivable may be placed on nonaccrual status earlier if, in management’s opinion, a timely collection of the full principal and interest becomes uncertain. After a note receivable has been placed in nonaccrual status, interest will be recognized when cash is received. A note receivable may be returned to accrual status after all of the customer’s delinquent balances of principal and interest have been settled, and collection of all remaining contractual amounts due is reasonably assured.
Inventory	Inventory Our inventory, which is comprised of raw materials and finished goods, includes materials used to produce our wireless communications network enabled radios, video cameras, home automation system parts and peripherals, is stated at the lower of cost or net realizable value, and is charged to cost of sales on a first in, first out, or FIFO, basis when the inventory is shipped from our manufacturer and received by our service provider partners. We periodically evaluate our inventory quantities for obsolescence based on criteria such as customer demand and changing technology and record an obsolescence write-off when necessary.
Internal-Use Software	Internal-Use Software We capitalize the costs directly related to the development of internal-use software for our platforms during the application development stage of the projects. Such costs primarily include payroll and payroll-related costs for engineers and product development employees directly associated with the development project. Our internal-use software is reported at cost less accumulated depreciation. Depreciation begins once the project is ready for its intended use, which is usually when the code goes into production in weekly software builds on our platforms. We depreciate the asset on a straight-line basis over a period of three years, which is the estimated useful life. We update our software for our SaaS multi-tenant platforms on a weekly basis utilizing continuous agile development methods, which primarily consists of bug-fixes and user interface changes. We evaluate whether a project should be capitalized if it adds significant functionality to our platforms. Maintenance activities or minor upgrades are expensed in the period performed.
External Software	External Software Costs incurred in researching and developing a computer software product that will be marketed and sold are charged to expense when incurred until technological feasibility is established. Technological feasibility is established upon completion of a detailed program design or, in its absence, completion of a working model (a beta version). After technological feasibility is established, certain payroll and payroll-related costs are capitalized for engineers and product development employees directly associated with the development project. Cost capitalization ceases when the product is available for general release. Our non-hosted software is typically developed in an agile environment with frequent revisions to product release features and functions. Agile development results in a short duration between completion of the detailed program design and beta release. Research and Development Our research and development costs consist primarily of personnel and related expenses for our employees working on our product development and software and device engineering teams, including salaries, bonuses, stock-based compensation, benefits and other personnel costs. Our research and development of new products and services is a multidisciplinary effort across our product management, program management, software engineering, device engineering, quality engineering, configuration management and network operations teams. Also included are non-personnel costs, such as consulting and professional fees paid to third-party development resources. We invest substantial resources in research and development to enhance our platforms and applications, support our technology infrastructure, develop new capabilities and conduct quality assurance testing.
Revenue Recognition and Deferred Revenue	Revenue Recognition and Deferred Revenue We derive our revenue from three primary sources: the sale of cloud-based SaaS services on our integrated Alarm.com platform, the sale of licenses and services on our non-hosted software platform, or Software platform, and the sale of hardware products. We sell our platform and hardware solutions to service provider partners that resell our solutions and hardware to residential and commercial property owners, who are the service provider partners’ customers. Our subscribers consist of all of the properties maintained by those residential and commercial property owners to which we are delivering at least one of our solutions. We also sell our hardware to distributors who resell the hardware to service provider partners. We enter into contracts with our service provider partners that establish pricing for access to our platform solutions and for the sale of hardware. These contracts typically have an initial term of one year, with subsequent renewal terms of one year. Our service provider partners typically enter into contracts with our subscribers, which our service provider partners have indicated range from three to five years in length. Our hardware includes cellular radio modules that enable access to our cloud-based platforms, as well as video cameras, image sensors and other peripherals. Our service provider partners may purchase our hardware in anticipation of installing the hardware in a residential or commercial property when they create a new subscriber account, or for use in existing subscriber properties. The purchase of hardware occurs in a transaction that is separate and typically in advance of the purchase of our platform services. The performance obligation is satisfied when the hardware is received by our service provider partner or distributor. Service provider partners transact with us to purchase our platform solutions and resell our solutions to a new subscriber, or to upgrade or downgrade the solutions of an existing subscriber, at which time the subscriber’s access to our platform solutions is enabled and the delivery of the services commences. Our performance obligation related to providing our platform solutions is satisfied on a daily basis as the subscriber uses the platform services. The purchase of platform solutions and the purchase of hardware are separate transactions as revenue is recognized when control of the promised goods or services are transferred to our customers, in an amount that reflects the consideration that we expect to receive in exchange for those goods or services. We generate all of our revenue from contracts with customers. SaaS and license revenue associated with our contracts is invoiced and revenue is recognized at an amount that corresponds directly with the value of the performance completed to date. Additionally, the consideration received from hardware sales corresponds directly with the stand-alone selling price of the hardware. As a result, we have elected to use the practical expedient related to the amount of transaction price allocated to the unsatisfied performance obligations and therefore, we have not disclosed the total remaining revenue expected to be recognized on all contracts or the expected period over which the remaining revenue would be recognized for the current period or any period presented before January 1, 2018. To determine the transaction price, we analyze all of the performance obligations included in the contract. We consider the terms of the contract and our customary business practices, which typically do not include financing components or non-cash consideration. We have variable consideration in the form of retrospective volume discounts, rebate incentives, restocking fees and assurance-type warranties. The significant inputs related to variable consideration include the volume and amount of products and services sold historically and expected to be sold in the future, the availability and performance of our services and the historical and expected number of returns. Depending on the type of variable consideration and its predictability, we may apply an "expected value" approach or a "most likely amount" approach. We estimate the variable consideration at the onset of a contract and include the variable consideration within the transaction price if it is probable that a significant reversal of the variable consideration would not occur in the future. When determining whether the amount of variable consideration included in the transaction price should be constrained, we look at the history of hardware purchased and subscribers added by our service provider partners to estimate the likelihood of those service provider partners obtaining the retrospective volume discounts and rebates. At times, our contracts include consideration payable to a customer in the form of fixed discounts or rebates. We record the consideration payable to a customer as a reduction to the transaction price resulting in a reduction to revenue over the service period. If we enter into contracts that contain multiple promised services, we evaluate which of the promised services represent separate performance obligations based on whether or not the promised services are distinct and whether or not the services are separable from other promises in the contract. If these criteria are met, then we allocate the transaction price to the performance obligations using the relative stand-alone selling price method at contract inception. In determining the relative estimated selling prices, we consider market conditions, entity-specific factors and information about the customer or class of customer. Any discount within the contract is allocated proportionately to all of the separate performance obligations in the contract unless the terms of discount relate specifically to the entity’s efforts to satisfy some but not all of the performance obligations. For our standard service provider agreements, we have used a portfolio approach for purposes of revenue recognition, as each agreement has similar characteristics and we do not expect the effects of applying this approach would have a material impact on our financial statements as compared to assessing each agreement individually. SaaS and License Revenue We generate the majority of our SaaS and license revenue primarily from monthly fees charged to our service provider partners sold on a per subscriber basis for access to our cloud-based intelligently connected property platform and related solutions. Our fees per subscriber vary based upon the service plan and features utilized. Under the terms of our contractual arrangements with our service provider partners, we bill a monthly fee to our service provider partners in advance of the month of service, with the exception of the initial partial month of service, which is paid in arrears. Due to the limited period of time between receipt of payment and delivery of service, we have not accounted for these advance payments as significant financing components. We typically transfer the promised SaaS services to our customers over time, which is evidenced by the fact that the customers receive and consume the benefits provided by our performance of the services as such services are rendered. As a result, we recognize revenue from SaaS services on a monthly basis as we satisfy our performance obligations. We have demonstrated that we can sell our SaaS offering on a stand-alone basis, as it can be sold separately from hardware and activation services. As there is neither a minimum required initial service term nor a stated renewal term in our contractual arrangements, we recognize revenue over the period of service, which is monthly. Our service provider partners typically incur and pay the same monthly fee per subscriber account for the entire period a subscriber account is active. We offer multiple service level packages for our platform solutions including a range of solutions and a range of a la carte add-ons for additional features. The fee paid by our service provider partners each month for the delivery of our solutions is based on the combination of packages and add-ons enabled for each subscriber. We utilize tiered pricing plans where our service provider partners may receive prospective pricing discounts driven by volume. We also generate SaaS and license revenue from the fees paid to us when we license our intellectual property to third parties for use of our patents. We bill a monthly fee to third parties based on the number of customers that were active during the prior month. We apply the usage-based royalty exception to recognize license revenue because the sole or predominant item to which the royalty relates is the license of intellectual property. Under the usage-based royalty exception, we recognize revenue on a monthly basis over the period of service. In addition, in certain markets our EnergyHub subsidiary sells its demand response service for an annual service fee, with pricing based on the number of subscribers or amount of aggregate electricity demand made available for a utility’s or market’s control. Software License Revenue Our SaaS and license revenue also includes our software license revenue from monthly fees charged to service providers sold on a per subscriber basis for access to our Software platform. The non-hosted software for interactive security, automation and related solutions is typically deployed and operated by the service provider in its own network operations center. Our agreements for the Software platform solution typically include software and services, such as post-contract customer support, or PCS. Software sales that include multiple elements are typically allocated to the various elements using the relative stand-alone selling price method. We apply the usage-based royalty exception to recognize license revenue associated with software hosted by our customers because the predominant item to which the royalty relates is the license of intellectual property. Under the usage-based royalty exception, we recognize revenue on a monthly basis over the period during which the services are expected to be performed. Under the terms of our contractual arrangements with our service provider partners, we are entitled to payment of a monthly fee that is billed per subscriber for the month of service. Our software license revenue during the years ended December 31, 2018, 2017 and 2016 was $41.3 million, $29.7 million and $0, respectively. Hardware and Other Revenue We generate hardware and other revenue primarily from the sale of video cameras and cellular radio modules that provide access to our cloud-based platforms and, to a lesser extent, the sale of other devices, including image sensors and peripherals. We primarily transfer hardware to our customers upon delivery to the customer, which corresponds with the time at which the customer obtains control of the hardware. As a result, we recognize hardware and other revenue as we satisfy our performance obligations, which occurs when the hardware is received by our service provider partner or distributor, net of a reserve for estimated returns. There are a few contracts in which we provide shipping and handling services to the customer after control of the hardware transfers to the customer. In these instances, we have elected to account for shipping and handling costs as activities performed to fulfill the promise to transfer hardware to the customer and not as a separate promised service. Amounts due from the sale of hardware are payable in accordance with the terms of our agreements with our service provider partners or distributors, and are not contingent on resale to end-users, or to service provider partners in the case of sales of hardware to distributors. Payment for our hardware is typically due within 30 days from shipment, with the exception of certain hardware finance arrangements, which are paid over a 36-month period. Our distributors sell directly to our service provider partners under terms between the two parties. When determining the amount of consideration we expect to be entitled to for the sale of our hardware, we estimate the variable consideration associated with customer returns. We record a reserve against revenue for hardware returns based on historical returns. For each of the years ended December 31, 2018, 2017 and 2016, our reserve against revenue for hardware returns was 2% of hardware and other revenue. We evaluate our hardware reserve on a quarterly basis or if there is an indication of significant changes in return experience. Historically, our returns of hardware have not significantly differed from our estimated reserve. Additionally, we provide assurance-type warranties related to the intended functionality of the products and services provided and those warranties typically allow for the return of hardware up to one year past the date of sale. These warranties were not identified as separate performance obligations. Hardware and other revenue may also include activation fees charged to some of our service provider partners for activation of a new subscriber account on our platforms, as well as fees paid by service provider partners for our marketing services. Our service provider partners use services on our platforms, such as support tools and applications, to assist in the installation of our solutions in subscriber properties. This installation marks the beginning of the service period on our platforms and, on occasion, we earn activation revenue for fees charged for this service. The activation fee is non-refundable, separately negotiated and specified in our contractual arrangements with our service provider partners and is charged to the service provider partner for each subscriber activated on our platforms. The decision whether to charge an activation fee is based in part on the expected number of subscribers to be added by our service provider partners and as a result, many of our largest service provider partners do not pay an activation fee. Activation fees are not offered on a stand-alone basis separate from our SaaS offering and are billed and received at the beginning of the arrangement. We record activation fees initially as deferred revenue and we recognize these fees ratably over the expected term of the subscribers’ account which we estimate is ten years based on our annual attrition rate. The portion of these activation fees included in current and long-term deferred revenue as of our balance sheet date represents the amounts that will be recognized ratably as revenue over the following twelve months, or longer as appropriate, until the ten-year expected term is complete.
Cost of Revenue	Cost of Revenue Our cost of SaaS and license revenue primarily includes the amounts paid to wireless network providers and, to a lesser extent, the costs of running our network operations centers which are expensed as incurred, as well as patent and royalty costs in connection with technology licensed from third-party providers. Our cost of SaaS and license revenue also includes our cost of software license revenue, which primarily includes the payroll and payroll-related costs of the department dedicated to providing service exclusively to those service providers that host the Software platform. Our cost of software license revenue during the years ended December 31, 2018, 2017 and 2016 was $1.7 million, $1.2 million and $0, respectively. Our cost of hardware and other revenue primarily includes cost of raw materials, tooling and amounts paid to our third-party manufacturer for production and fulfillment of our cellular radio modules and image sensors, and procurement costs for our video cameras, which we purchase from an original equipment manufacturer, and other devices. Our cost of hardware and other revenue also includes royalty costs in connection with technology licensed from third-party providers. We record the cost of SaaS and license revenue as expenses are incurred, which corresponds to the delivery period of our services to our subscribers. We record the cost of hardware and other revenue when the hardware and other services are delivered to the service provider partner, which occurs when control of the hardware and other services transfers to the service provider partner. Our cost of revenue excludes amortization and depreciation. Contract Asset and Contract Liability Balances At contract inception, we assess the goods and services promised in our contracts with customers and identify a performance obligation for each distinct promise to transfer a good or service, or bundle of goods or services. To identify the performance obligations, we consider all of the goods or services promised in the contract, whether explicitly stated or implied based on customary business practices. We record a contract asset when we satisfy a performance obligation by transferring a promised good or service. Contract assets can be conditional or unconditional depending on whether another performance obligation must be satisfied before payment can be received. We receive payments from our service provider partners based on the billing schedule established in our contracts. All of the accounts receivable presented in the balance sheet represent unconditional rights to consideration. We do not have any assets from contracts containing conditional rights and we do not have any assets from satisfied performance obligations that have not been invoiced. We recognize an asset related to the costs incurred to obtain a contract only if we expect to recover those costs and we would not have incurred those costs if the contract had not been obtained. We recognize an asset from the costs incurred to fulfill a contract if the costs (i) are specifically identifiable to a contract, (ii) enhance resources that will be used in satisfying performance obligations in future and (iii) are expected to be recovered. Our contract assets consist of capitalized commission costs. Based on the policy above, we capitalize a portion of our commission costs as an incremental cost of obtaining a contract. When calculating the incremental cost of obtaining a contract, we exclude any commission costs related to metrics that could be satisfied without obtaining a contract, including training-related metrics. We amortize our commission costs over a period of three years, which is consistent with the period over which the products and services related to the commission are transferred to the customer. The three-year period was determined based on our review of historical enhancements and upgrades to our products and services. We applied the portfolio approach to account for the amortization of contract costs as each contract has similar characteristics. The current portion of capitalized commission costs is included in other current assets within our consolidated balance sheets. The non-current portion of capitalized commission costs is reflected in other assets within our consolidated balance sheets. We amortized capitalized commission costs of $2.0 million during the year ended December 31, 2018. There were no amortized commission costs during the years ended December 31, 2017 and 2016. We review the capitalized costs for impairment at least annually. Impairment exists if the carrying amount of the asset recognized from contract costs exceeds the remaining amount of consideration we expect to receive in exchange for providing the goods and services to which such asset relates, less the costs that relate directly to providing those good and services and that have not been recognized as an expense. We did not record an impairment loss on our capitalized commission costs or any other contract assets during the years ended December 31, 2018, 2017 and 2016. Contract liabilities include payments received in advance of performance under the contract, and are realized with the associated revenue recognized under the contract. All of the deferred revenue presented in the balance sheet represents contract liabilities resulting from advance cash receipts from customers or amounts billed in advance to customers from the sale of services. Changes in deferred revenue are due to our performance under the contract as well as to cash received from new contracts for which services have not been provided.
Fair Value Measurements	Fair Value Measurements The accounting standard for fair value measurements provides a framework for measuring fair value and requires disclosures regarding fair value measurements. Fair value is defined as the price that would be received for an asset or the exit price that would be paid to transfer a liability in the principal or most advantageous market in an orderly transaction between market participants on the measurement date. This accounting standard established a fair value hierarchy, which requires an entity to maximize the use of observable inputs, where available. The following summarizes the three levels of inputs: Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity can access at the measurement date; Level 2 - Inputs other than quoted prices included within Level 1 that are observable for similar assets and liabilities, either directly or indirectly; quoted prices in markets that are not active; and Level 3 - Unobservable inputs supported by little or no market activity. The carrying amount of financial assets, including cash and cash equivalents, accounts receivable and accounts payable approximates fair value because of the short maturity and liquidity of those instruments. Assets and Liabilities Measured at Fair Value on a Recurring Basis - in 2018, 2017 and 2016, we recorded liabilities for subsidiary unit awards and a contingent consideration liability related to acquisitions at fair value on a recurring basis. Assets Measured at Fair Value on a Nonrecurring Basis - We measure certain assets, including property and equipment, goodwill, intangible and long-lived assets, cost and equity method investments at fair value on a nonrecurring basis. These assets are recognized at fair value when they are deemed to be other-than-temporarily impaired. The liability for the subsidiary unit awards relates to agreements established with employees of our subsidiaries for cash awards contingent upon the subsidiary companies meeting certain financial milestones such as revenue, working capital, EBITDA and EBITDA margin. We account for these subsidiary awards using fair value and establish liabilities for the future payment for the repurchase of subsidiary units under the terms of the agreements based on estimating revenue, working capital, EBITDA and EBITDA margin of the subsidiary units over the periods of the awards through the anticipated repurchase dates. We estimated the fair value of each liability by using a Monte Carlo simulation model for determining each of the projected measures by using an expected distribution of potential outcomes. The fair value of each liability is calculated with thousands of projected outcomes, the results of which are averaged and then discounted to estimate the present value. At each reporting date until the respective payment dates, we will remeasure these liabilities, using the same valuation approach based on the applicable subsidiary's revenue and future collection of financed customer receivables, the unobservable inputs, and we will record any changes in the employee's compensation expense. Some of the awards are subject to the employees' continued employment and therefore recorded on a straight-line basis over the remaining service period.
Concentration of Credit Risk	Concentration of Credit Risk The financial instruments that potentially subject us to concentrations of credit risk consists principally of cash and cash equivalents and accounts receivables. All of our cash and cash equivalents are held at financial institutions that management believes to be of high credit quality. Our cash and cash equivalent accounts may exceed federally insured limits at times. We have not experienced any losses on cash and cash equivalents to date. To manage accounts receivable risk, we evaluate the credit worthiness of our service provider partners and maintain an allowance for doubtful accounts. The majority of our accounts receivable balance is due from our service provider partners in North America. We assess the concentrations of credit risk with respect to accounts receivables based on one industry and geographic region and believe that our reserve for uncollectible accounts is appropriate based on our history and this concentration.
Stock-Based Compensation	Stock-Based Compensation We compensate our executive officers, board of directors, employees and consultants with stock-based compensation plans under our 2015 Equity Incentive Plan, or 2015 Plan. We record stock-based compensation expense based upon the award’s grant date fair value and use an accelerated attribution method, net of actual forfeitures, in which compensation cost for each vesting tranche in an award is recognized ratably from the service inception date to the vesting date for that tranche. Our equity awards generally vest over five years and are settled in shares of our common stock. During 2018, 2017 and 2016, we recognized compensation expense of $13.4 million, $7.4 million and $4.0 million, respectively, and associated income tax benefit of $7.6 million, $12.7 million and $5.0 million, respectively, in connection with our stock-based compensation plans. We account for stock-based compensation arrangements with non-employees using a fair value approach. The fair value of these options is measured using the Black-Scholes option pricing model reflecting the same assumptions as applied to employee options in each of the reported periods, other than the expected life, which is assumed to be the remaining contractual life of the option. Our Employee Stock Purchase Plan, or 2015 ESPP, allows eligible employees to purchase shares of our common stock at 90% of the fair market value of the closing price on the purchase date. The maximum number of shares of our common stock that a participant may purchase during any calendar year is limited to the lesser of 10% of the participant's base compensation for that year or the number of shares with a fair market value of $15,000. The 2015 ESPP is considered compensatory for purposes of share-based compensation expense. Compensation expense is recognized for the amount of the discount, net of actual forfeitures, over the six-month purchase period. We value our stock options using the Black-Scholes option pricing model, which requires the input of subjective assumptions, including the risk-free interest rate, expected term, expected stock price volatility and dividend yield. The risk-free interest rate assumption is based upon observed interest rates for constant maturity U.S. Treasury securities consistent with the expected term of our stock options. The expected term represents the period of time the stock options are expected to be outstanding and is based on the "simplified method." Under the "simplified method," the expected term of an option is presumed to be the mid-point between the vesting date and the end of the contractual term. We use the "simplified method" due to the lack of sufficient historical exercise data to provide a reasonable basis upon which to otherwise estimate the expected term of the stock options. Expected volatility is based on historical volatilities of our stock and publicly traded stock of comparable companies over the estimated expected term of the stock options.
401(k) Defined Contribution Plan	401(k) Defined Contribution Plan We adopted the Alarm.com Holdings 401(k) Plan, or the Plan, on April 30, 2009. All of our employees are eligible to participate in the Plan. For the year ended December 31, 2018, our discretionary match was 100% of employee contributions up to 10% of salary and up to a $4,000 maximum match. For the years ended December 31, 2017 and 2016, our discretionary match was 100% of employee contributions up to 6% of salary and up to a $3,000 maximum match.
Business Combinations	Business Combinations We are required to allocate the purchase price of acquired companies to the identifiable tangible and intangible assets acquired and liabilities assumed at the acquisition date based upon their estimated fair values. The net assets and results of operations of an acquired entity are included in our consolidated financial statements from the acquisition date. Acquisition-related costs are expensed as incurred. Goodwill as of the acquisition date represents the excess of the purchase consideration of an acquired business over the fair value of the underlying net tangible and intangible assets acquired net of liabilities assumed. This allocation and valuation require management to make significant estimates and assumptions, especially with respect to long-lived and intangible assets. Critical estimates in valuing intangible assets include, but are not limited to, estimates about future expected cash flows from customer contracts, customer lists, proprietary technology and non-competition agreements, the acquired company’s brand awareness and market position, assumptions about the period of time the brand will continue to be used in our solutions, as well as expected costs to develop the in-process research and development into commercially viable products and estimated cash flows from the projects when completed, and discount rates. Our estimates of fair value are based upon assumptions we believe to be reasonable, but which are inherently uncertain and unpredictable. Assumptions may be incomplete or inaccurate, and unanticipated events and circumstances may occur. Other estimates associated with the accounting for these acquisitions may change as additional information becomes available regarding the assets acquired and liabilities assumed.
Goodwill, Intangible Assets and Long-lived Assets	Goodwill, Intangible Assets and Long-lived Assets Goodwill Goodwill represents the excess of (1) the aggregate of the fair value of consideration transferred in a business combination, over (2) the fair value of assets acquired, net of liabilities assumed. Goodwill is allocated to our reporting units, which are our operating segments or one level below our operating segments. Goodwill is not amortized, but is subject to annual impairment tests. We perform our annual impairment review of goodwill on October 1 and when a triggering event occurs between annual impairment tests. We test our goodwill at the reporting unit level. We perform either a qualitative analysis or a quantitative analysis every year depending on the changes to our goodwill balance as well as changes in our business and the economy. Qualitative factors we consider include, but are not limited to, macroeconomic conditions, industry and market conditions, company specific events, changes in circumstances and market capitalization. The amount of goodwill impairment is calculated as the amount by which a reporting unit's carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. For our 2018 annual impairment review, we performed a quantitative assessment for our Alarm.com reporting unit, our only reporting unit with a goodwill balance. Based on the results of our qualitative assessment, we determined that it was not more likely than not that the fair value of our reporting unit was less than its carrying amount, including goodwill. Therefore, we concluded that there was no goodwill impairment as of October 1, 2018. Our assessment was performed as of October 1, 2018, and we have determined there have been no triggering events from our assessment date through December 31, 2018. Intangible Assets and Long-lived Assets Intangible assets are initially valued at fair value using generally accepted valuation methods appropriate for the type of intangible asset. Intangible assets with definite lives are amortized over their estimated useful lives. We evaluate the recoverability of our intangible assets with definite lives and long-lived assets for impairment whenever events or circumstances indicate that the carrying amount of the assets may not be recoverable. Recoverability of intangible assets with definite lives and long-lived assets are measured by comparison of the carrying amount of the asset to the future undiscounted cash flows the asset is expected to generate. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset.
Advertising Costs	Advertising Costs We expense advertising costs as incurred. Advertising costs totaled $11.4 million, $4.1 million and $4.6 million for the years ended December 31, 2018, 2017 and 2016, respectively. Advertising costs are included within sales and marketing expenses on our consolidated statements of operations.
Accounting for Income Taxes	Accounting for Income Taxes We account for income taxes under the asset and liability method as required by accounting standards codification, or ASC 740, "Income Taxes," which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that are included in the financial statements. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. We record net deferred tax assets to the extent we believe these assets will more likely than not be realized. In making such a determination, we consider all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. During 2013, in connection with the EnergyHub acquisition, we acquired significant net operating losses, a deferred tax asset, which we recorded at its expected realizable value. Based on our historical and expected future taxable earnings, we believe it is more likely than not that we will realize all of the benefit of the existing deferred tax assets as of December 31, 2018 and 2017. Accordingly, we have not recorded a valuation allowance as of December 31, 2018 and 2017. We are subject to income taxes in the United States and foreign jurisdictions based upon our business operations in those jurisdictions. Significant judgment is required in evaluating uncertain tax positions. We record uncertain tax positions in accordance with ASC 740-10 on the basis of a two-step process whereby (1) we determine whether it is more likely than not that the tax positions will be sustained based on the technical merits of the position, and (2) with respect to those tax positions that meet the more-likely-than-not recognition threshold, we recognize the largest amount of tax benefit that is greater than 50% likely to be realized upon ultimate settlement with the related tax authority. We record interest and penalties as a component of our income tax provision. We recognize a valuation allowance if, based on the weight of available evidence, both positive and negative, it is more likely than not that some portion, or all, of net deferred tax assets will not be realized. We apply guidance for uncertainty in income taxes that requires the application of a more likely than not threshold to the recognition and de-recognition of uncertain tax positions. If the recognition threshold is met, this guidance permits us to recognize a tax benefit measured at the largest amount of the tax benefit that, in our judgment, is more likely than not to be realized upon settlement.
Earnings per Share, or EPS	Earnings per Share, or EPS Our basic net income per share attributable to common stockholders is calculated by dividing the net income attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. Our diluted net income per share attributable to common stockholders is calculated by giving effect to all potentially dilutive common stock when determining the weighted-average number of common shares outstanding. For purposes of the diluted net income per share calculation, options to purchase common stock, redeemable convertible preferred stock, restricted stock units and unvested shares issued upon the early exercise of options that are subject to repurchase are considered to be potential common stock. We have issued securities other than common stock that participate in dividends ("participating securities"), and therefore utilize the two-class method to calculate net income per share. These participating securities include redeemable convertible preferred stock and unvested shares issued upon the early exercise of options that are subject to repurchase, both of which have non-forfeitable rights to participate in any dividends declared on our common stock. The two-class method requires a portion of net income to be allocated to the participating securities to determine the net income attributable to common stockholders. Net income attributable to the common stockholders is equal to the net income less dividends paid on redeemable convertible preferred stock and unvested shares with any remaining earnings allocated in accordance with the bylaws between the outstanding common and preferred stock as of the end of each period.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Adopted Revenue from Contracts with Customers (Topic 606): In May 2014, the Financing Accounting Standards Board, or FASB, and International Accounting Standards Board jointly issued Accounting Standards Update, or ASU, 2014-09, "Revenue from Contracts with Customers (Topic 606)," a new revenue recognition standard that provides a framework for addressing revenue issues, improves the comparability of revenue recognition practices across industries, provides useful information to users of financial statements through improved disclosure requirements and simplifies the presentation of financial statements. From March to December 2016, amendments to Topic 606 were issued to clarify numerous accounting topics, including, but not limited to: (i) the implementation guidance on principal versus agent considerations, (ii) the identification of performance obligations, (iii) the licensing implementation guidance, (iv) the objective of the collectibility criterion, (v) the application of the variable consideration guidance and modified retrospective transition method, (vi) the way in which impairment testing is performed and (vii) the disclosure requirements for revenue recognized from performance obligations. This guidance permits the use of either a full retrospective method or a modified retrospective method. This guidance was effective beginning January 1, 2018. On January 1, 2018, we adopted Topic 606 by applying the modified retrospective transition method to all of our contracts. Comparative information has not been restated and continues to be reported under the accounting standards in effect for the periods presented. The adoption of Topic 606 did not have a material impact on our revenue recognition policies, however, as a result of adopting the new standard, we changed our treatment of commissions paid to employees, which we previously expensed as incurred. Under the new standard, we capitalize a portion of our commission costs as an incremental cost of obtaining a contract and amortize our commission costs over a period of three years, which is consistent with the period over which the products and services related to the commission are transferred to the customer. Based on the results of our evaluation, the adoption of Topic 606 did not have a material impact on our consolidated financial statements for the year ended December 31, 2018. Additionally, the cumulative effect to the opening balance sheet on January 1, 2018 from the adoption of Topic 606 was not material. Other Accounting Standards: On May 10, 2017, the FASB issued ASU 2017-09, "Compensation - Stock Compensation (Topic 718) - Scope of Modification Accounting," which amends the scope of modification accounting for share-based payment arrangements. The update provides guidance on the types of changes to the terms or conditions of share-based payment awards to which an entity would be required to apply modification accounting under Accounting Standards Codification, or ASC, Topic 718. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. The amendment is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted. We adopted ASU 2017-09 during the first quarter of 2018 and the adoption of this ASU did not have a material impact on our financial statements and related disclosures. On January 5, 2017, the FASB issued ASU 2017-01, "Business Combinations (Topic 805) - Clarifying the Definition of a Business," which provides guidance to assist entities in evaluating when a set of transferred assets and activities is a business. To be considered a business, an acquisition would have to include an input and a substantive process that together significantly contribute to the ability to create outputs. The amendment is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted. We adopted ASU 2017-01 during the first quarter of 2018 and the adoption of this ASU did not have a material impact on our financial statements and related disclosures. In January 2016, the FASB issued ASU 2016-01, "Recognition and Measurement of Financial Assets and Financial Liabilities (Topic 825-10)" and in February 2018, the FASB issued ASU 2018-03, "Technical Corrections and Improvements to Financial Instruments - Overall (Subtopic 825-10)." These ASUs require entities to carry all investments in equity securities at fair value and recognize any changes in fair value in net income. Under these standards, equity investments that do not have readily determinable fair values are measured at cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for an identical or a similar investment of the same issuer. The guidance in ASU 2016-01 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The guidance in ASU 2018-03 is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years beginning after June 15, 2018. We adopted ASU 2016-01 and ASU 2018-03 in 2018 and the adoption of these ASUs did not have a material impact on our financial statements and related disclosures. Not Yet Adopted On June 16, 2016, the FASB issued ASU 2016-13, "Financial Instruments - Credit Losses (Topic 326)," which provides guidance designed to provide financial statement users with more information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. When determining such expected credit losses, the guidance requires companies to apply a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. The amendment is effective on a modified retrospective basis for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. Early adoption is permitted for fiscal years and interim periods beginning after December 15, 2018. We are currently assessing the impact this pronouncement may have on our trade receivables and notes receivables. On February 25, 2016, the FASB issued ASU 2016-02, "Leases (Topic 842)" or Topic 842, which requires lessees to recognize operating and financing lease liabilities and corresponding right-of-use assets on the balance sheet. The update also requires improved disclosures to help users of financial statements better understand the amount, timing and uncertainty of cash flows arising from leases. The amendments in this update are effective for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. We plan to adopt Topic 842 effective January 1, 2019. The update must be adopted using a modified retrospective approach. In July 2018, the FASB amended the update to allow entities to apply the transition requirements of Topic 842 at the adoption date rather than at the beginning of the earliest comparative period presented. We plan to use this optional transition method, which will require us to record the effect of initially applying Topic 842 as a cumulative-effect adjustment to retained earnings on January 1, 2019. We plan to use the package of practical expedients for the adoption of Topic 842, which will allow us not to reassess: (i) whether any expired or existing contracts are or contain leases, (ii) lease classification for any expired or existing leases and (iii) whether initial direct costs for any existing leases qualify for capitalization under Topic 842. Additionally, we plan to use the hindsight practical expedient when determining the lease term and assessing impairment of right-of-use assets. While we are still evaluating the impact the update will have on our consolidated financial statements, we estimate that the adoption of Topic 842 will result in the recognition of approximately $28.4 million of leased right-of-use assets, $1.1 million of property and equipment, $29.4 million of lease liabilities, net of the reduction to deferred rent liability, and less than $0.1 million as a reduction of accumulated deficit, within the consolidated balance sheets as of January 1, 2019. We do not expect the adoption of Topic 842 to have a material impact on our consolidated statements of operations. On August 28, 2018, the FASB issued ASU 2018-13, "Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement," which provides guidance designed to improve the effectiveness of fair value measurement disclosures in notes to the financial statements. The update removes several existing disclosure requirements, including, but not limited to: (i) the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, (ii) the policy for timing of transfers between levels and (iii) the valuation processes for Level 3 fair value measurements. The update also adds additional disclosure requirements for public companies, including but not limited to: (i) the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and (ii) the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. The update also modifies and clarifies several existing disclosure requirements. The amendment in this update is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years. The additional disclosure requirements and one of the modifications to an existing disclosure requirement should be applied prospectively while all other disclosure changes should be applied retrospectively to all periods presented upon the effective date. Early adoption is permitted. We are currently assessing the impact this pronouncement may have on our fair value measurement disclosures; however, this pronouncement is not expected to have a material impact on our consolidated financial statements.
Property and Equipment, Net	Property and Equipment, Net Furniture and fixtures, computer software and equipment, leasehold improvements and real property are recorded at cost and presented net of depreciation. We record land at historical cost. During the application development phase, we record capitalized development costs in our construction in progress account and then reclass the asset to internal-use software when the project is ready for its intended use, which is usually when the code goes into production. Furniture and fixtures and computer software and equipment are depreciated on a straight-line basis over lives ranging from three to five years. Internal-use software is amortized on a straight-line basis over a three-year period. Leasehold improvements are amortized on a straight-line basis over the shorter of the lease terms or the asset lives. Real property is amortized on a straight-line basis over 15 years.
Leases	We recognize rent expense for lease payments on a straight-line basis over the expected lease term and amortize tenant improvement allowances over the term of the lease.