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			19,832					19,832
Exercise of stock options	$ 5		23,479					23,484
Exercise of stock options (in shares)	389,000
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					35,318			35,318
Other comprehensive income (loss)-other						641		641
Balance at Sep. 30, 2019	$ 541	$ (1,464,727)	1,371,718	$ (144)	1,454,623	317	$ (144)	1,362,472
Balance (in shares) at Sep. 30, 2019	54,131,000	(29,662,000)
Balance at Jun. 30, 2019	$ 541	$ (1,464,727)	1,364,693		1,433,348	415		1,334,270
Balance (in shares) at Jun. 30, 2019	54,063,000	(29,662,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			4,811					4,811
Exercise of stock options			5					5
Issuance of equity			2,209					2,209
Issuance of equity (in shares)	68,000
Net income					21,274			21,274
Other comprehensive income (loss)-other					1	(98)		(97)
Balance at Sep. 30, 2019	$ 541	$ (1,464,727)	1,371,718	(144)	1,454,623	317	(144)	1,362,472
Balance (in shares) at Sep. 30, 2019	54,131,000	(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			18,854					$ 18,854
Exercise of stock options	$ 9		48,639					$ 48,648
Exercise of stock options (in shares)	803,000							804,523
Issuance of equity	$ 1		900					$ 901
Issuance of equity (in shares)	181,000
Net income					113,402			113,402
Other comprehensive income (loss)-other						(23)		(23)
Balance at Sep. 30, 2020	$ 553	$ (1,464,727)	1,455,009	(413)	1,588,196	121	(413)	$ 1,579,152
Balance (in shares) at Sep. 30, 2020	55,269,000	(29,662,000)						25,607,000
Balance at Jun. 30, 2020	$ 550	$ (1,464,727)	1,429,995		1,576,549	602		$ 1,542,969
Balance (in shares) at Jun. 30, 2020	54,972,000	(29,662,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			5,839					5,839
Exercise of stock options	$ 3		17,138					17,141
Exercise of stock options (in shares)	263,000
Issuance of equity			2,037					2,037
Issuance of equity (in shares)	34,000
Net income					11,647			11,647
Other comprehensive income (loss)-other						(481)		(481)
Balance at Sep. 30, 2020	$ 553	$ (1,464,727)	$ 1,455,009	$ (413)	$ 1,588,196	$ 121	$ (413)	$ 1,579,152
Balance (in shares) at Sep. 30, 2020	55,269,000	(29,662,000)						25,607,000