Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at Dec. 31, 2015	$ 195,566	$ 34	$ 223,228	$ (211)	$ (27,485)
Balance (in shares) at Dec. 31, 2015		34,414,631
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,224				19,224
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	55			55
Change in unrealized loss on investments	55
Issuance of common stock upon exercise of stock options	$ 15,157	$ 2	15,155
Issuance of common stock upon exercise of stock options (shares)	1,399,157	1,399,157
Issuance of common stock upon vesting of restricted stock units (in shares)		25,213
Excess tax benefits from stock-based compensation	$ 8,700		8,700
Issuance of common stock in exchange for services	26		26
Issuance of common stock in exchange for services (shares)		2,000
Taxes from release of the restricted share units	(438)		(438)
Stock-based compensation	20,123		20,123
Balance at Dec. 31, 2016	258,413	$ 36	266,794	(156)	(8,261)
Balance (in shares) at Dec. 31, 2016		35,841,001
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,440
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(418)
Change in unrealized loss on investments	(418)
Issuance of common stock upon exercise of stock options	$ 31,327	$ 3	31,324
Issuance of common stock upon exercise of stock options (shares)	2,997,095	2,997,095
Issuance of common stock upon vesting of restricted stock units (in shares)		217,111
Taxes from release of the restricted share units	$ (20,924)		(20,924)
Taxes related to net share settlement of equity awards, shares		(457,090)
Stock-based compensation	26,961		26,961
Balance at Dec. 31, 2017	343,544	$ 39	304,155	(574)	39,924
Balance (in shares) at Dec. 31, 2017		38,598,117
Accumulated deficit	39,924
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	57,304				57,304
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(12)			(12)
Change in unrealized loss on investments	28
Issuance of common stock upon exercise of stock options	$ 24,053	$ 1	24,052
Issuance of common stock upon exercise of stock options (shares)	1,183,235	1,183,235
Stock Repurchased During Period, Shares		(1,088,899)
Treasury Stock, Value, Acquired, Cost Method	$ (85,040)	$ (1)	(13,064)		(71,975)
Issuance of common stock upon vesting of restricted stock units (in shares)		524,903
Taxes from release of the restricted share units	(14,879)		(14,879)
Stock-based compensation	30,308		30,308
Balance at Dec. 31, 2018	357,989	$ 39	$ 330,572	$ (586)	$ 27,964
Balance (in shares) at Dec. 31, 2018		39,015,034
Accumulated deficit	$ 27,964