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, 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)
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
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)
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)
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
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			19,384					$ 19,384
Exercise of stock options	$ 4		17,754					$ 17,758
Exercise of stock options (in shares)	277,000							276,392
Issuance of equity	$ 1		(1,438)					$ (1,437)
Issuance of equity (in shares)	168,000
Accretion of non-controlling interest					(5,033)			(5,033)
Net income					33,097			33,097
Other comprehensive income (loss)-other						161		161
Balance at Sep. 30, 2021	$ 560	$ (1,464,727)	1,512,919		1,885,194	(44)		$ 1,933,902
Balance (in shares) at Sep. 30, 2021	55,994,000	(29,662,000)						26,332,000
Balance at Jun. 30, 2021	$ 559	$ (1,464,727)	1,503,718		1,884,291	(20)		$ 1,923,821
Balance (in shares) at Jun. 30, 2021	55,927,000	(29,662,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			5,974					5,974
Exercise of stock options	$ 1		3,485					3,486
Exercise of stock options (in shares)	54,000
Issuance of equity			(258)					(258)
Issuance of equity (in shares)	13,000
Accretion of non-controlling interest					(5,033)			(5,033)
Net income					5,936			5,936
Other comprehensive income (loss)-other						(24)		(24)
Balance at Sep. 30, 2021	$ 560	$ (1,464,727)	$ 1,512,919		$ 1,885,194	$ (44)		$ 1,933,902
Balance (in shares) at Sep. 30, 2021	55,994,000	(29,662,000)						26,332,000