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, 2018	$ 535	$ (1,461,002)	$ 1,326,645		$ 1,419,449	$ (324)		$ 1,285,303
Balance (in shares) at Dec. 31, 2018	53,536,000	(29,601,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			15,021					15,021
Exercise of stock options	$ 5		23,474					23,479
Exercise of stock options (in shares)	389,000
Issuance of equity	$ 1		(447)					(446)
Issuance of equity (in shares)	138,000
Repurchase of stock		$ (3,725)						(3,725)
Repurchase of stock (in shares)		(61,000)
Net income					14,044			14,044
Other comprehensive income (loss)-other						739		739
Balance at Jun. 30, 2019	$ 541	$ (1,464,727)	1,364,693	$ (145)	1,433,348	415	$ (145)	1,334,270
Balance (in shares) at Jun. 30, 2019	54,063,000	(29,662,000)
Balance at Mar. 31, 2019	$ 537	$ (1,464,727)	1,337,849		1,419,735	(4)		1,293,390
Balance (in shares) at Mar. 31, 2019	53,695,000	(29,662,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			5,414					5,414
Exercise of stock options	$ 4		21,430					21,434
Exercise of stock options (in shares)	348,000
Issuance of equity (in shares)	20,000
Net income					13,613			13,613
Other comprehensive income (loss)-other						419		419
Balance at Jun. 30, 2019	$ 541	$ (1,464,727)	1,364,693	(145)	1,433,348	415	(145)	1,334,270
Balance (in shares) at Jun. 30, 2019	54,063,000	(29,662,000)
Balance at Dec. 31, 2019	$ 543	$ (1,464,727)	1,386,616		1,475,207	144		$ 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			13,015					$ 13,015
Exercise of stock options	$ 6		31,501					$ 31,507
Exercise of stock options (in shares)	540,000							541,148
Issuance of equity	$ 1		(1,137)					$ (1,136)
Issuance of equity (in shares)	147,000
Net income					101,755			101,755
Other comprehensive income (loss)-other						458		458
Balance at Jun. 30, 2020	$ 550	$ (1,464,727)	1,429,995	(413)	1,576,549	602	(413)	$ 1,542,969
Balance (in shares) at Jun. 30, 2020	54,972,000	(29,662,000)						25,310,000
Balance at Mar. 31, 2020	$ 546	$ (1,464,727)	1,402,797		1,493,044	(57)		$ 1,431,603
Balance (in shares) at Mar. 31, 2020	54,631,000	(29,662,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			6,958					6,958
Exercise of stock options	$ 4		20,240					20,244
Exercise of stock options (in shares)	324,000
Issuance of equity (in shares)	17,000
Net income					83,505			83,505
Other comprehensive income (loss)-other						659		659
Balance at Jun. 30, 2020	$ 550	$ (1,464,727)	$ 1,429,995	$ (413)	$ 1,576,549	$ 602	$ (413)	$ 1,542,969
Balance (in shares) at Jun. 30, 2020	54,972,000	(29,662,000)						25,310,000