Basis of Presentation (Policies)	9 Months Ended
Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying condensed consolidated financial statements include the accounts of Simpson Manufacturing Co., Inc. and its subsidiaries (collectively, the “Company”). Investments in 50% or less owned entities are accounted for using either cost or the equity method. All significant intercompany transactions have been eliminated.
Interim Period Reporting	Interim Reporting Period The accompanying unaudited quarterly condensed consolidated financial statements have been prepared pursuant to the rules and regulations for reporting on Form 10-Q. Accordingly, certain information and footnotes required by accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted. These interim statements should be read in conjunction with the audited consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018 (the “2018 Form 10-K”). The unaudited quarterly condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, contain all adjustments (consisting of only normal recurring adjustments) necessary to state fairly the financial information set forth therein in accordance with GAAP. Certain prior period amounts in the condensed consolidated financial statements and the accompanying notes have been reclassified to conform to the current period’s presentation. The year-end condensed consolidated balance sheet data provided herein were derived from audited financial statements included in the 2018 Form 10-K, but do not include all disclosures required by GAAP. The Company’s quarterly results fluctuate. As a result, the Company believes the results of operations for this interim period presented are not indicative of the results to be expected for any future periods.
Revenue Recognition	Revenue Recognition Generally, the Company's revenue contract with a customer exists when the goods are shipped, services are rendered; and its related invoice is generated. The duration of the contract does not extend beyond the promised goods or services already transferred. The transaction price of each distinct promised product or service specified in the invoice is based on its relative stated standalone selling price. The Company recognizes revenue when it satisfies a performance obligation by transferring control over a product to a customer at a point in time. The Company’s shipping terms provide the primary indicator of the transfer of control. The Company's general shipping terms are F.O.B. shipping point, where title and risk and rewards of ownership transfer at the point when the products leave the Company's warehouse. The Company recognizes revenue based on the consideration specified in the invoice with a customer, excluding any sales incentives, discounts, and amounts collected on behalf of third parties (i.e., governmental tax authorities). Based on historical experience with the customer, the customer's purchasing pattern and its significant experience selling products, the Company concluded that a significant reversal in the cumulative amount of revenue recognized will not occur when the uncertainty (if any) is resolved (that is, when the total amount of purchases is known). Refer to Note 2 for additional information.
Net Income Per Common Share	Net Income Per Common Share The Company calculates net income per common share based on the weighted-average number of the Company's common stock outstanding during the period. Potentially dilutive securities are included in the diluted per-share calculations using the treasury stock method for all periods when the effect is dilutive.
Accounting for Leases	Accounting for Leases The Company has operating and finance leases for certain facilities, equipment, autos and data centers. As an accounting policy for short-term leases, the Company elected to not recognize the right-of-use asset and liability, if, at the commencement date, the lease (1) has a term of 12 months or less and (2) does not include renewal and purchase options that the Company is reasonably certain to exercise. Monthly payments on short-term leases are recognized on the straight-line basis over the full lease term.
Accounting for Stock-Based Compensation	Accounting for Stock-Based Compensation The Company recognizes stock-based expense related to restricted stock unit awards on a straight-line basis, net of estimated forfeitures, over the requisite service period of the awards, which is generally a vesting term of four years. Stock-based expense related to performance share grants are measured based on the grant date fair value and expensed on a graded basis over the service periods of the awards, which is generally a performance period of three years. The assumptions used to calculate the fair value of options or restricted stock units are evaluated and revised, as necessary, to reflect market conditions and the Company's experienc
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or a liability. Assets and liabilities recorded at fair value are measured and classified under a three-tier fair valuation hierarchy based on the observability of the inputs available in the market: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2 inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument; and Level 3 inputs are unobservable inputs based on the Company’s assumptions used to measure assets and liabilities at fair value. The fair value hierarchy requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. As of September 30, 2019 and 2018, the Company’s investments included in cash equivalents consisted of only money market funds, which are the Company’s primary financial instruments and carried at cost, approximating fair value, based on Level 1 inputs. The balance of the Company’s primary financial instruments as of September 30, 2019 and 2018 was $0.1 million and $7.6 million, respectively. The carrying amounts of trade accounts receivable, accounts payable and accrued liabilities approximate fair value due to the short-term nature of these instruments. The fair value of the Company’s contingent consideration related to acquisitions is classified as Level 3 within the fair value hierarchy as it is based on unobserved inputs such as management estimates and entity-specific assumptions and is evaluated on an ongoing basis.
Income Taxes	Income Taxes The Company uses an estimated annual tax rate to measure the tax benefit or tax expense recognized in each interim period.
Acquisitions	Acquisitions Under the business combinations topic ASC 805, the Company accounts for acquisitions as business combinations and ascribes acquisition-date fair values to the acquired assets and assumed liabilities. Provisional fair value measurements are made at the time of the acquisition. Adjustments to those measurements may be made in subsequent periods, up to one year from the acquisition date, as information necessary to complete the analysis is obtained. The fair value of intangible assets are generally based on Level 3 inputs.
Recently Adopted Accounting Standards and Recently Issued Accounting Standards Not Yet Adopted	Accounting Standards - To Be Adopted In June 2016, the FASB issued ASU No. 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” ASU 2016-13 amendments provide guidance on accounting for current expected credit losses on financial instruments that are not accounted for at fair value through net income, including loans held for investment, held-to-maturity debt securities, trade and other receivables, net investment in leases and other commitments to extend credit held by a reporting entity at each reporting date. The required measurement methodology is based on expected loss model that includes historical experience, current conditions, and reasonable and supportable forecasts. ASU 2016-13 eliminates the probable incurred loss recognition in current GAAP. ASU 2016-13 is effective for interim and annual periods beginning after December 15, 2019. Early adoption is permitted for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. The Company is evaluating the impact of the adoption of this new accounting guidance on its consolidated financial statements. Accounting Standards - Recently Adopted In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”). The core requirement of ASU 2016-02 is to recognize assets and liabilities that arise from leases, including those leases classified as operating leases. The amendments require a lessee to recognize a liability to make lease payments (the lease liability) and a right-of-use asset ("ROU") representing its right to use the underlying asset for the lease term in the statement of financial position. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted. On January 1, 2019, the Company adopted ASU 2016-02 using the optional transition method. The Company elected and applied a few practical transition expedients including, not reassessing whether any expired or existing contracts are or contain leases; not reassessing the lease classification for any expired or existing leases and not reassessing initial direct costs for any existing leases. The Company has operating and finance leases for certain facilities, equipment, autos and data centers. The adoption of ASU 2016-02 resulted in the recognition of ROU assets and lease liabilities of approximately $34.3 million and $35.1 million, respectively on January 1, 2019. The adoption had no material impact on the condensed consolidated statement of operations or cash flows. See Note 10. All other issued and effective accounting standards during the third quarter of 2019 were determined to be not relevant or material to the Company.

Basis of Presentation (Policies)

9 Months Ended

Sep. 30, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The accompanying condensed consolidated financial statements include the accounts of Simpson Manufacturing Co., Inc. and its subsidiaries (collectively, the “Company”). Investments in 50% or less owned entities are accounted for using either cost or the equity method. All significant intercompany transactions have been eliminated.

Interim Period Reporting

Interim Reporting Period

The accompanying unaudited quarterly condensed consolidated financial statements have been prepared pursuant to the rules and regulations for reporting on Form 10-Q. Accordingly, certain information and footnotes required by accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted. These interim statements should be read in conjunction with the audited consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018 (the “2018 Form 10-K”).

The unaudited quarterly condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements and, in the opinion of management, contain all adjustments (consisting of only normal recurring adjustments) necessary to state fairly the financial information set forth therein in accordance with GAAP. Certain prior period amounts in the condensed consolidated financial statements and the accompanying notes have been reclassified to conform to the current period’s presentation. The year-end condensed consolidated balance sheet data provided herein were derived from audited financial statements included in the 2018 Form 10-K, but do not include all disclosures required by GAAP. The Company’s quarterly results fluctuate. As a result, the Company believes the results of operations for this interim period presented are not indicative of the results to be expected for any future periods.

Revenue Recognition

Generally, the Company's revenue contract with a customer exists when the goods are shipped, services are rendered; and its related invoice is generated. The duration of the contract does not extend beyond the promised goods or services already transferred. The transaction price of each distinct promised product or service specified in the invoice is based on its relative stated standalone selling price. The Company recognizes revenue when it satisfies a performance obligation by transferring control over a product to a customer at a point in time. The Company’s shipping terms provide the primary indicator of the transfer of control. The Company's general shipping terms are F.O.B. shipping point, where title and risk and rewards of ownership transfer at the point when the products leave the Company's warehouse. The Company recognizes revenue based on the consideration specified in the invoice with a customer, excluding any sales incentives, discounts, and amounts collected on behalf of third parties (i.e., governmental tax authorities). Based on historical experience with the customer, the customer's purchasing pattern and its significant experience selling products, the Company concluded that a significant reversal in the cumulative amount of revenue recognized will not occur when the uncertainty (if any) is resolved (that is, when the total amount of purchases is known). Refer to Note 2 for additional information.

Net Income Per Common Share

The Company calculates net income per common share based on the weighted-average number of the Company's common stock outstanding during the period. Potentially dilutive securities are included in the diluted per-share calculations using the treasury stock method for all periods when the effect is dilutive.

Accounting for Leases

The Company has operating and finance leases for certain facilities, equipment, autos and data centers. As an accounting policy for short-term leases, the Company elected to not recognize the right-of-use asset and liability, if, at the commencement date, the lease (1) has a term of 12 months or less and (2) does not include renewal and purchase options that the Company is reasonably certain to exercise. Monthly payments on short-term leases are recognized on the straight-line basis over the full lease term.

Accounting for Stock-Based Compensation

The Company recognizes stock-based expense related to restricted stock unit awards on a straight-line basis, net of estimated forfeitures, over the requisite service period of the awards, which is generally a vesting term of four years. Stock-based expense related to performance share grants are measured based on the grant date fair value and expensed on a graded basis over the service periods of the awards, which is generally a performance period of three years. The assumptions used to calculate the fair value of options or restricted stock units are evaluated and revised, as necessary, to reflect market conditions and the Company's experienc

Fair Value of Financial Instruments

Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or a liability. Assets and liabilities recorded at fair value are measured and classified under a three-tier fair valuation hierarchy based on the observability of the inputs available in the market: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2 inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument; and Level 3 inputs are unobservable inputs based on the Company’s assumptions used to measure assets and liabilities at fair value. The fair value hierarchy requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value.

As of September 30, 2019 and 2018, the Company’s investments included in cash equivalents consisted of only money market funds, which are the Company’s primary financial instruments and carried at cost, approximating fair value, based on Level 1 inputs. The balance of the Company’s primary financial instruments as of September 30, 2019 and 2018 was $0.1 million and $7.6 million, respectively. The carrying amounts of trade accounts receivable, accounts payable and accrued liabilities approximate fair value due to the short-term nature of these instruments. The fair value of the Company’s contingent consideration related to acquisitions is classified as Level 3 within the fair value hierarchy as it is based on unobserved inputs such as management estimates and entity-specific assumptions and is evaluated on an ongoing basis.

Income Taxes

The Company uses an estimated annual tax rate to measure the tax benefit or tax expense recognized in each interim period.

Acquisitions

Under the business combinations topic ASC 805, the Company accounts for acquisitions as business combinations and ascribes acquisition-date fair values to the acquired assets and assumed liabilities. Provisional fair value measurements are made at the time of the acquisition. Adjustments to those measurements may be made in subsequent periods, up to one year from the acquisition date, as information necessary to complete the analysis is obtained. The fair value of intangible assets are generally based on Level 3 inputs.

Recently Adopted Accounting Standards and Recently Issued Accounting Standards Not Yet Adopted

Accounting Standards - To Be Adopted

In June 2016, the FASB issued ASU No. 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” ASU 2016-13 amendments provide guidance on accounting for current expected credit losses on financial instruments that are not accounted for at fair value through net income, including loans held for investment, held-to-maturity debt securities, trade and other receivables, net investment in leases and other commitments to extend credit held by a reporting entity at each reporting date. The required measurement methodology is based on expected loss model that includes historical experience, current conditions, and reasonable and supportable forecasts. ASU 2016-13 eliminates the probable incurred loss recognition in current GAAP. ASU 2016-13 is effective for interim and annual periods beginning after December 15, 2019. Early adoption is permitted for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. The Company is evaluating the impact of the adoption of this new accounting guidance on its consolidated financial statements.

Accounting Standards - Recently Adopted

In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”). The core requirement of ASU 2016-02 is to recognize assets and liabilities that arise from leases, including those leases classified as operating leases. The amendments require a lessee to recognize a liability to make lease payments (the lease liability) and a right-of-use asset ("ROU") representing its right to use the underlying asset for the lease term in the statement of financial position. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted. On January 1, 2019, the Company adopted ASU 2016-02 using the optional transition method. The Company elected and applied a few practical transition expedients including, not reassessing whether any expired or existing contracts are or contain leases; not reassessing the lease classification for any expired or existing leases and not reassessing initial direct costs for any existing leases. The Company has operating and finance leases for certain facilities, equipment, autos and data centers. The adoption of ASU 2016-02 resulted in the recognition of ROU assets and lease liabilities of approximately $34.3 million and $35.1 million, respectively on January 1, 2019. The adoption had no material impact on the condensed consolidated statement of operations or cash flows. See Note 10.

All other issued and effective accounting standards during the third quarter of 2019 were determined to be not relevant or material to the Company.