Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	1.625% Convertible Senior Notes due May 2018 [Member] Additional Paid-in Capital [Member]	1.625% Convertible Senior Notes due May 2018 [Member]	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2013			53,565	55,523,636
Balance at Dec. 31, 2013			$ 1	$ 555	$ 1,357,037	$ 111,367	$ 0	$ 1,468,960
Net income						215,865		215,865
Stock issuances under employee plans, including income tax benefits (in shares)				512,602
Stock issuances under employee plans, including income tax benefits				$ 5	20,170			20,175
Repurchase and retirement of common stock, net of expenses (in shares)				(1,008,000)
Repurchase and retirement of common stock, net of expenses				$ (10)	(36,771)			(36,781)
Amortization of stock-based compensation					8,469			8,469
Balance (in shares) at Dec. 31, 2014			53,565	55,028,238
Balance at Dec. 31, 2014			$ 1	$ 550	1,348,905	327,232	0	1,676,688
Net income						213,509		213,509	[1]
Stock issuances under employee plans, including income tax benefits (in shares)				1,350,984
Stock issuances under employee plans, including income tax benefits				$ 13	10,237			10,250
Repurchase and retirement of common stock, net of expenses (in shares)				(645,338)
Repurchase and retirement of common stock, net of expenses				$ (6)	(22,067)			(22,073)
Amortization of stock-based compensation					15,624			15,624
Balance (in shares) at Dec. 31, 2015				121,286,153
Balance at Dec. 31, 2015			$ 0	$ 1,213	3,324,328	535,890	5	3,861,436
Other comprehensive income, net of tax							5	5
Common stock dividends ($0.04 per share)						(4,851)		(4,851)
Stock issuance in connection with merger, net of preferred stock conversion (in shares)			(53,565)	65,552,269
Stock issuance in connection with merger, net of preferred stock conversion			$ (1)	$ 656	1,971,629			1,972,284
Net income						484,730		484,730	[1]
Stock issuances under employee plans, including income tax benefits (in shares)				396,489
Stock issuances under employee plans, including income tax benefits				$ 4	1,326			1,330
Repurchase and retirement of common stock, net of expenses (in shares)				(7,253,345)
Repurchase and retirement of common stock, net of expenses				$ (73)	(232,447)			(232,520)
Amortization of stock-based compensation					17,794			17,794
Balance (in shares) at Dec. 31, 2016				114,429,297
Balance at Dec. 31, 2016			$ 0	$ 1,144	$ 3,204,835	1,001,779	(172)	4,207,586
Other comprehensive income, net of tax							$ (177)	(177)
Common stock dividends ($0.04 per share)						$ (18,841)		$ (18,841)
1.625% convertible note conversion feature purchase accounting adjustment	$ 93,834	$ 93,834

[1] Per share amounts do not add across due to rounding differences in quarterly amounts and due to the impact of differences between the quarterly and annual weighted average share calculations.