CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss), Net	Retained Earnings (Deficit)
Beginning Balance (in shares) at Dec. 31, 2014		80,205
Beginning Balance at Dec. 31, 2014	$ 752,771	$ 8	$ 783,410	$ (140)	$ (30,507)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	144,020				144,020
Net change in unrealized gains (losses) from investments	(686)			(686)
Net change in foreign currency translation adjustment	(164)		(10)	(154)
Issuance of common stock relating to employee equity compensation plans (in shares)		991
Issuance of common stock relating to employee equity compensation plans	11,325	$ 0	11,325
Tax withholdings related to net share settlements of restricted stock units	(20,716)		(20,716)
Common stock repurchased and retired (shares)		(1,696)
Common stock repurchased and retired	(101,791)		(15,669)		(86,122)
Net tax benefits from stock-based awards	10,224		10,224
Stock-based compensation	52,943		52,943
Ending Balance (in shares) at Dec. 31, 2015		79,500
Ending Balance at Dec. 31, 2015	847,926	$ 8	821,507	(980)	27,391
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	189,682				189,682
Net change in unrealized gains (losses) from investments	712			712
Net change in foreign currency translation adjustment	(670)		0	(670)
Issuance of common stock relating to employee equity compensation plans (in shares)		1,163
Issuance of common stock relating to employee equity compensation plans	13,778	$ 0	13,778
Tax withholdings related to net share settlements of restricted stock units	(29,857)		(29,857)
Common stock repurchased and retired (shares)		(1,110)
Common stock repurchased and retired	(96,218)		(10,593)		(85,625)
Net tax benefits from stock-based awards	15,888		15,888
Stock-based compensation	54,148		54,148
Ending Balance (in shares) at Dec. 31, 2016		79,553
Ending Balance at Dec. 31, 2016	995,389	$ 8	864,871	(938)	131,448
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	231,418
Net change in unrealized gains (losses) from investments	(232)			(232)
Net change in foreign currency translation adjustment	1,741			1,741
Issuance of common stock relating to employee equity compensation plans (in shares)		1,073
Issuance of common stock relating to employee equity compensation plans	14,461		14,461
Tax withholdings related to net share settlements of restricted stock units	(46,168)		(46,168)
Common stock repurchased and retired (shares)		(586)
Common stock repurchased and retired	(103,793)		(5,583)		(98,210)
Stock-based compensation	58,854		58,854
Ending Balance (in shares) at Dec. 31, 2017		80,040
Ending Balance at Dec. 31, 2017	1,150,370	$ 8	$ 886,435	$ 571	$ 263,356
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment from adoption of ASU 2016-16	$ (1,300)