CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Common Stock In Treasury	Additional Paid in Capital	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings	Accumulated Other Comprehensive (Loss) Income	Cumulative Effect, Period of Adoption, Adjustment	Total
Balance at Dec. 31, 2017	$ 530	$ (1,397,962)	$ 1,274,811	$ (4,227)	$ 1,399,495	$ (380)	$ (4,227)	$ 1,276,494
Balance (in shares) at Dec. 31, 2017	52,973,000	(28,771,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			29,472					29,472
Exercise of stock options	$ 4		23,060					$ 23,064
Exercise of stock options (in shares)	409,000							409,208
Issuance of equity	$ 1		(698)					$ (697)
Issuance of equity (in shares)	154,000
Repurchase of stock		$ (63,040)						(63,040)
Repurchase of stock (in shares)		(830,000)
Net income					24,181			24,181
Other comprehensive income (loss)-other						56		56
Balance at Dec. 31, 2018	$ 535	$ (1,461,002)	1,326,645	(144)	1,419,449	(324)	(144)	1,285,303
Balance (in shares) at Dec. 31, 2018	53,536,000	(29,601,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			25,501					25,501
Exercise of stock options	$ 7		32,708					$ 32,715
Exercise of stock options (in shares)	543,000							543,752
Issuance of equity	$ 1		1,762					$ 1,763
Issuance of equity (in shares)	206,000
Repurchase of stock		$ (3,725)						(3,725)
Repurchase of stock (in shares)		(61,000)
Net income					55,902			55,902
Other comprehensive income (loss)-other						468		468
Balance at Dec. 31, 2019	$ 543	$ (1,464,727)	1,386,616	$ (412)	1,475,207	144	$ (412)	$ 1,397,783
Balance (in shares) at Dec. 31, 2019	54,285,000	(29,662,000)						24,623,000
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			25,450					$ 25,450
Exercise of stock options	$ 11		64,518					$ 64,529
Exercise of stock options (in shares)	1,041,000							1,042,186
Issuance of equity	$ 1		635					$ 636
Issuance of equity (in shares)	223,000
Net income					382,335			382,335
Other comprehensive income (loss)-other						(349)		(349)
Balance at Dec. 31, 2020	$ 555	$ (1,464,727)	$ 1,477,219		$ 1,857,130	$ (205)		$ 1,869,972
Balance (in shares) at Dec. 31, 2020	55,549,000	(29,662,000)						25,887,000