Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings (Deficit) [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Retained Earnings (Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Total
Balance at beginning of period at Dec. 31, 2018	$ 790	$ 1,262,063	$ (1,410)	$ (909,186)	$ 0	$ (1,410)	$ 353,667
Balance (in shares) at Dec. 31, 2018	79,044
Net income				674,833			674,833	[1]
Total other comprehensive income (loss)							0
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes		8,053					8,053
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	25
Net issuance of common stock upon exercise of stock options	$ 2	19,926					19,928
Net issuance of common stock upon exercise of stock options, shares	181
Share-based compensation		10,328					10,328
Share repurchases, including fees	$ (25)	(41,440)		(879,252)			$ (920,717)
Share repurchases, including fees, shares	(2,560)						(2,560,000)
Balance at end of period at Jun. 30, 2019	$ 767	1,258,930		(1,115,015)	0		$ 144,682
Balance (in shares) at Jun. 30, 2019	76,690
Balance at beginning of period at Mar. 31, 2019	$ 783	1,268,032		(896,450)	0		372,365
Balance (in shares) at Mar. 31, 2019	78,262
Net income				353,681			353,681
Total other comprehensive income (loss)							0
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes		4,281					4,281
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	13
Net issuance of common stock upon exercise of stock options		7,973					7,973
Net issuance of common stock upon exercise of stock options, shares	48
Share-based compensation		5,243					5,243
Share repurchases, including fees	$ (16)	(26,599)		(572,246)			$ (598,861)
Share repurchases, including fees, shares	(1,633)						(1,633,000)
Balance at end of period at Jun. 30, 2019	$ 767	1,258,930		(1,115,015)	0		$ 144,682
Balance (in shares) at Jun. 30, 2019	76,690
Balance at beginning of period at Dec. 31, 2019	$ 756	1,280,760		(889,066)	4,890		$ 397,340	[2]
Balance (in shares) at Dec. 31, 2019	75,619						75,618,659
Net income				832,105			$ 832,105
Total other comprehensive income (loss)					(27,001)		(27,001)
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes		8,922					8,922
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	27
Net issuance of common stock upon exercise of stock options	$ 2	17,981					17,983
Net issuance of common stock upon exercise of stock options, shares	121
Share-based compensation		10,778					10,778
Share repurchases, including fees	$ (17)	(28,465)		(622,545)			$ (651,027)
Share repurchases, including fees, shares	(1,669)						(1,669,000)
Balance at end of period at Jun. 30, 2020	$ 741	1,289,976		(679,506)	(22,111)		$ 589,100
Balance (in shares) at Jun. 30, 2020	74,098						74,097,706
Balance at beginning of period at Mar. 31, 2020	$ 742	1,271,250		(1,137,392)	(25,756)		$ 108,844
Balance (in shares) at Mar. 31, 2020	74,199
Net income				531,667			531,667
Total other comprehensive income (loss)					3,645		3,645
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes		4,818					4,818
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	15
Net issuance of common stock upon exercise of stock options	$ 1	11,846					11,847
Net issuance of common stock upon exercise of stock options, shares	69
Share-based compensation		5,254					5,254
Share repurchases, including fees	$ (2)	(3,192)		(73,781)			$ (76,975)
Share repurchases, including fees, shares	(185)						(185,000)
Balance at end of period at Jun. 30, 2020	$ 741	$ 1,289,976		$ (679,506)	$ (22,111)		$ 589,100
Balance (in shares) at Jun. 30, 2020	74,098						74,097,706

[1] Note: Certain prior period amounts have been reclassified to conform to current period presentation.

[2] The balance sheet at December 31, 2019, has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by United States generally accepted accounting principles for complete financial statements.