Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Balance, beginning at Dec. 31, 2014	$ 770,522	$ 8	$ 689,953	$ (262)	$ 80,823
Balance, beginning (in shares) at Dec. 31, 2014		81,905,325
Net income	38,077				38,077
Currency translation	(342)			(342)
Stock-based compensation	13,955		13,955
Tax benefit related to stock-based compensation	27,830		27,830
Stock option exercises, net of withholdings and other	11,919		11,919
Stock option exercises, net of withholdings and other (in shares)		2,578,398
Issuance of restricted stock awards (in shares)		101,616
Issuance of common stock, acquisitions	15,980		15,980
Issuance of common stock, acquisitions (in shares)		407,812
Shares repurchased and retired to satisfy tax withholding upon vesting	(345)		(345)
Shares repurchased and retired to satisfy tax withholding upon vesting (in shares)		(13,282)
Balance, ending at Dec. 31, 2015	877,596	$ 8	759,292	(604)	118,900
Balance, ending (in shares) at Dec. 31, 2015		84,979,869
Net income	49,557				49,557
Currency translation	(1,474)			(1,474)
Stock-based compensation	25,619		25,619
Tax benefit related to stock-based compensation	24,906		24,906
Stock option exercises and vesting of restricted stock units, net of withholdings and other	13,468	$ 1	13,467
Stock option exercises and vesting of restricted stock units, net of withholdings and other (in shares)		1,523,952
Repurchases of common stock	(14,774)		(14,774)
Repurchases of common stock (shares)		(724,473)
Shares repurchased and retired to satisfy tax withholding upon vesting	(2,779)		(2,779)
Shares repurchased and retired to satisfy tax withholding upon vesting (in shares)		(87,015)
Balance, ending at Dec. 31, 2016	972,119	$ 9	805,731	(2,078)	168,457
Balance, ending (in shares) at Dec. 31, 2016		85,692,333
Net income	98,983				98,983
Cumulative effect adjustment upon adoption of ASU 2016-09	2,552				2,552
Currency translation	850			850
Stock-based compensation	$ 37,219		37,219
Stock option exercises, net of withholdings and other (in shares)	728,710
Stock option exercises and vesting of restricted stock units, net of withholdings and other	$ 16,375		16,375
Stock option exercises and vesting of restricted stock units, net of withholdings and other (in shares)		1,331,083
Issuance of common stock, acquisitions	274		274
Shares repurchased and retired to satisfy tax withholding upon vesting	(10,556)		(10,556)
Shares repurchased and retired to satisfy tax withholding upon vesting (in shares)		(232,792)
Balance, ending at Dec. 31, 2017	$ 1,117,816	$ 9	$ 849,043	$ (1,228)	$ 269,992
Balance, ending (in shares) at Dec. 31, 2017		86,790,624