Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings (Deficit) [Member]	Accumulated Other Comprehensive Income [Member]	Total
Cumulative effective adjustment from adoption of ASU | Adoption of ASU 2016-09 [Member]		$ 434	$ (266)		$ 168
Balance at beginning of period at Dec. 31, 2016	$ 929	1,336,707	289,500	$ 0	1,627,136
Balance (in shares) at Dec. 31, 2016	92,852,000
Net income			1,133,804		1,133,804
Other comprehensive income					0
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes		13,466			13,466
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	66,000
Net issuance of common stock upon exercise of stock options	$ 7	33,222			33,229
Net issuance of common stock upon exercise of stock options, shares	685,000
Share based compensation		17,773			17,773
Share repurchases, including fees	$ (93)	(136,559)	(2,035,878)		(2,172,530)
Share repurchases, including fees, shares	(9,301,000)
Balance at end of period at Dec. 31, 2017	$ 843	1,265,043	(612,840)	0	653,046
Balance (in shares) at Dec. 31, 2017	84,302,000
Net income			1,324,487		1,324,487
Other comprehensive income				0	0
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes		14,173			14,173
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	58,000
Net issuance of common stock upon exercise of stock options	$ 8	57,160			57,168
Net issuance of common stock upon exercise of stock options, shares	745,000
Share based compensation		18,806			18,806
Share repurchases, including fees	$ (61)	(93,119)	(1,620,833)		$ (1,714,013)
Share repurchases, including fees, shares	(6,061,000)				(6,061,000)
Balance at end of period at Dec. 31, 2018	$ 790	1,262,063	(909,186)	0	$ 353,667
Balance (in shares) at Dec. 31, 2018	79,044,000				79,043,919
Cumulative effective adjustment from adoption of ASU | Adoption of ASU 2016-02 [Member]			(1,410)		$ (1,410)
Net income			1,391,042		1,391,042
Other comprehensive income				4,890	4,890
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes		15,302			15,302
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	46,000
Net issuance of common stock upon exercise of stock options	$ 5	46,101			46,106
Net issuance of common stock upon exercise of stock options, shares	406,000
Share based compensation		20,534			20,534
Share repurchases, including fees	$ (39)	(63,240)	(1,369,512)		$ (1,432,791)
Share repurchases, including fees, shares	(3,877,000)				(3,877,000)
Balance at end of period at Dec. 31, 2019	$ 756	$ 1,280,760	$ (889,066)	$ 4,890	$ 397,340
Balance (in shares) at Dec. 31, 2019	75,619,000				75,618,659