Stock Plans and Stock-Based Compensation - Stock Options - Additional Information (Details) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 9,299,000	$ 3,101,000	$ 1,522,000
Intrinsic value of options exercised	9,100,000	1,600,000	500,000
Intrinsic value of all outstanding options	32,100,000	15,900,000	10,100,000
Total unrecognized compensation cost	14,900,000	6,600,000
Proceeds from option exercises	$ 2,869,000	$ 750,000	$ 49,000
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average grant-date fair value per share of options granted	$ 22.84	$ 14.49	$ 12.19
Stock-based compensation expense	$ 5,300,000	$ 3,100,000	$ 1,500,000
Excess tax benefits realized from stock options exercised	$ 0	$ 0	$ 0
Weighted-average amortization period	2 years 11 months 19 days	2 years 7 months 2 days

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Unrecognized cost of unvested options awarded to employees as compensation.

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The aggregate cash inflow comprised of the amount received from (a) employees to acquire the entity's shares under incentive awards, including stock option exercises and restricted stock arrangements, and (b) the excess tax benefit arising from such transactions.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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