CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock Cumulative Effect, Period of Adoption, as Adjusted	Common Stock	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings Cumulative Effect, Period of Adoption, as Adjusted	Retained Earnings	Treasury Stock Cumulative Effect, Period of Adoption, as Adjusted	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, as Adjusted	Total
Balance at Dec. 31, 2019	$ 686,806	$ 686,806	$ (11,639)	$ 2,067,540	$ 2,079,179	$ (590,971)	$ (590,971)		$ (11,639)	$ 2,163,375	$ 2,175,014
Balance (in shares) at Dec. 31, 2019	81,743	81,743				(31,420)	(31,420)
Increase (Decrease) in Stockholders' Equity
Net income (loss)					29,988						29,988
Exercise of common stock options and vested employee stock awards		$ 38									38
Exercise of common stock options and vested employee stock awards (in shares)		287
Employee income tax paid on vested equity awards							$ (6,165)				(6,165)
Employee income tax paid on vested equity awards (in shares)							(108)
Sale of common stock under employee stock purchase plan		$ 1,494									1,494
Sale of common stock under employee stock purchase plan (in shares)		24
Stock based compensation expense		$ 1,727									1,727
Treasury stock purchases							$ (20,000)				(20,000)
Treasury stock purchases (in shares)							(386)
Cash dividends declared ($0.14 per share)					(7,019)						(7,019)
Balance at Mar. 31, 2020		$ 690,065			2,090,509		$ (617,136)				2,163,438
Balance (in shares) at Mar. 31, 2020		82,054					(31,914)
Balance at Dec. 31, 2019	$ 686,806	$ 686,806	$ (11,639)	$ 2,067,540	2,079,179	$ (590,971)	$ (590,971)		$ (11,639)	$ 2,163,375	2,175,014
Balance (in shares) at Dec. 31, 2019	81,743	81,743				(31,420)	(31,420)
Increase (Decrease) in Stockholders' Equity
Net income (loss)											37,935
Balance at Sep. 30, 2020		$ 703,780			2,098,456		$ (617,136)				2,185,100
Balance (in shares) at Sep. 30, 2020		82,095					(31,914)
Balance at Mar. 31, 2020		$ 690,065			2,090,509		$ (617,136)				2,163,438
Balance (in shares) at Mar. 31, 2020		82,054					(31,914)
Increase (Decrease) in Stockholders' Equity
Net income (loss)					(25,715)						(25,715)
Stock based compensation expense		$ 2,087									2,087
Warrants issued to U.S. Treasury		2,845									2,845
Net unrealized appreciation on marketable securities, net of tax								$ 307			307
Balance at Jun. 30, 2020		$ 694,997			2,064,794		$ (617,136)	307			2,142,962
Balance (in shares) at Jun. 30, 2020		82,054					(31,914)
Increase (Decrease) in Stockholders' Equity
Net income (loss)					33,662						33,662
Sale of common stock under employee stock purchase plan		$ 1,287									1,287
Sale of common stock under employee stock purchase plan (in shares)		41
Stock based compensation expense		$ 2,093									2,093
Warrants issued to U.S. Treasury		5,403									5,403
Net unrealized appreciation on marketable securities, net of tax								$ (307)			(307)
Balance at Sep. 30, 2020		$ 703,780			2,098,456		$ (617,136)				2,185,100
Balance (in shares) at Sep. 30, 2020		82,095					(31,914)
Balance at Dec. 31, 2020		$ 704,675			2,052,006		$ (617,136)				2,139,545
Balance (in shares) at Dec. 31, 2020		82,095					(31,914)
Increase (Decrease) in Stockholders' Equity
Net income (loss)					35,900						35,900
Exercise of common stock options and vested employee stock awards		$ 606									606
Exercise of common stock options and vested employee stock awards (in shares)		177
Employee income tax paid on vested equity awards							$ (1,573)				(1,573)
Employee income tax paid on vested equity awards (in shares)							(42)
Sale of common stock under employee stock purchase plan		$ 1,139									1,139
Sale of common stock under employee stock purchase plan (in shares)		30
Stock based compensation expense		$ 2,613									2,613
Warrants issued to U.S. Treasury		3,291									3,291
Balance at Mar. 31, 2021		$ 712,324			2,087,906		$ (618,709)				2,181,521
Balance (in shares) at Mar. 31, 2021		82,302					(31,956)
Balance at Dec. 31, 2020		$ 704,675			2,052,006		$ (617,136)				2,139,545
Balance (in shares) at Dec. 31, 2020		82,095					(31,914)
Increase (Decrease) in Stockholders' Equity
Net income (loss)											107,578
Balance at Sep. 30, 2021		$ 720,932			2,159,584		$ (618,709)				2,261,807
Balance (in shares) at Sep. 30, 2021		82,336					(31,956)
Balance at Mar. 31, 2021		$ 712,324			2,087,906		$ (618,709)				2,181,521
Balance (in shares) at Mar. 31, 2021		82,302					(31,956)
Increase (Decrease) in Stockholders' Equity
Net income (loss)					61,994						61,994
Stock based compensation expense		$ 2,877									2,877
Warrants issued to U.S. Treasury		2,513									2,513
Balance at Jun. 30, 2021		$ 717,714			2,149,900		$ (618,709)				2,248,905
Balance (in shares) at Jun. 30, 2021		82,302					(31,956)
Increase (Decrease) in Stockholders' Equity
Net income (loss)					9,684						9,684
Sale of common stock under employee stock purchase plan		$ 1,401									1,401
Sale of common stock under employee stock purchase plan (in shares)		34
Stock based compensation expense		$ 1,817									1,817
Balance at Sep. 30, 2021		$ 720,932			$ 2,159,584		$ (618,709)				$ 2,261,807
Balance (in shares) at Sep. 30, 2021		82,336					(31,956)