CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Common stock [Member]	Additional paid-in capital [Member]	Retained earnings (deficit) [Member]	Accumulated other comprehensive income (loss) [Member]	Total
Balance at beginning 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
Net income			1,359,357		1,359,357
Total other comprehensive income (loss)				(21,925)	(21,925)
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes		12,979			12,979
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	36,000
Net issuance of common stock upon exercise of stock options	$ 3	39,503			39,506
Net issuance of common stock upon exercise of stock options, shares	251,000
Share-based compensation		15,968			15,968
Share repurchases, including fees	$ (26)	(45,511)	(1,048,463)		$ (1,094,000)
Share repurchases, including fees, shares	(2,634,000)				(2,634,000)
Balance at end of period at Sep. 30, 2020	$ 733	1,303,699	(578,172)	(17,035)	$ 709,225
Balance (in shares) at Sep. 30, 2020	73,272,000
Balance at beginning of period at Jun. 30, 2020	$ 741	1,289,976	(679,506)	(22,111)	589,100
Balance (in shares) at Jun. 30, 2020	74,098,000
Net income			527,252		527,252
Total other comprehensive income (loss)				5,076	5,076
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes		4,057			4,057
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	9,000
Net issuance of common stock upon exercise of stock options	$ 1	21,522			21,523
Net issuance of common stock upon exercise of stock options, shares	130,000
Share-based compensation		5,190			5,190
Share repurchases, including fees	$ (9)	(17,046)	(425,918)		$ (442,973)
Share repurchases, including fees, shares	(965,000)				(965,000)
Balance at end of period at Sep. 30, 2020	$ 733	1,303,699	(578,172)	(17,035)	$ 709,225
Balance (in shares) at Sep. 30, 2020	73,272,000
Balance at beginning of period at Dec. 31, 2020	$ 711	1,280,841	(1,139,139)	(2,155)	$ 140,258	[1]
Balance (in shares) at Dec. 31, 2020	71,123,000				71,123,109
Net income			1,645,712		$ 1,645,712
Total other comprehensive income (loss)				(5,673)	(5,673)
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes	$ 1	14,152			14,153
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	32,000
Net issuance of common stock upon exercise of stock options	$ 3	54,488			54,491
Net issuance of common stock upon exercise of stock options, shares	331,000
Share-based compensation		17,367			17,367
Share repurchases, including fees	$ (38)	(70,490)	(1,936,633)		$ (2,007,161)
Share repurchases, including fees, shares	(3,801,000)				(3,801,000)
Balance at end of period at Sep. 30, 2021	$ 677	1,296,358	(1,430,060)	(7,828)	$ (140,853)
Balance (in shares) at Sep. 30, 2021	67,685,000				67,684,615
Balance at beginning of period at Jun. 30, 2021	$ 691	1,295,363	(1,075,769)	(2,591)	$ 217,694
Balance (in shares) at Jun. 30, 2021	69,133,000
Net income			558,652		558,652
Total other comprehensive income (loss)				(5,237)	(5,237)
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes	$ 1	4,722			4,723
Issuance of common stock under employee benefit plans, net of forfeitures and shares withheld to cover taxes, shares	10,000
Net issuance of common stock upon exercise of stock options	$ 1	20,718			20,719
Net issuance of common stock upon exercise of stock options, shares	125,000
Share-based compensation		5,568			5,568
Share repurchases, including fees	$ (16)	(30,013)	(912,943)		$ (942,972)
Share repurchases, including fees, shares	(1,583,000)				(1,583,000)
Balance at end of period at Sep. 30, 2021	$ 677	$ 1,296,358	$ (1,430,060)	$ (7,828)	$ (140,853)
Balance (in shares) at Sep. 30, 2021	67,685,000				67,684,615

[1] The balance sheet at December 31, 2020, 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.