CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Retained Earnings	Treasury Stock	Total
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		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, 2021	$ 722,310	2,163,916	$ (618,712)	2,267,514
Balance (in shares) at Dec. 31, 2021	82,336		(31,956)
Increase (Decrease) in Stockholders' Equity
Net income		17,734		17,734
Exercise of common stock options and vested employee stock awards	$ 27			27
Exercise of common stock options and vested employee stock awards (in shares)	139
Employee income tax paid on vested equity awards			$ (1,123)	(1,123)
Employee income tax paid on vested equity awards (in shares)			(37)
Sale of common stock under employee stock purchase plan	$ 1,487			1,487
Sale of common stock under employee stock purchase plan (in shares)	40
Stock based compensation expense	$ 4,076			4,076
Balance at Mar. 31, 2022	$ 727,900	$ 2,181,650	$ (619,835)	$ 2,289,715
Balance (in shares) at Mar. 31, 2022	82,515		(31,993)