CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Common Stock In Treasury	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total
Balance at Dec. 31, 2017	$ 530	$ (1,397,962)	$ 1,274,811	$ 1,399,495	$ (380)	$ 1,276,494
Balance (in shares) at Dec. 31, 2017	52,973,000	(28,771,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			18,085			18,085
Exercise of stock options	$ 4		21,472			21,476
Exercise of stock options (in shares)	379,000
Issuance of equity	$ 1		(3,052)			(3,051)
Issuance of equity (in shares)	123,000
Repurchase of stock		$ (14,823)				(14,823)
Repurchase of stock (in shares)		(149,000)
Net income				25,003		25,003
Other comprehensive income (loss)-other					(187)	(187)
Adoption of new accounting standards | Accounting Standards Update 2014-09				(4,227)		(4,227)
Balance at Jun. 30, 2018	$ 535	$ (1,412,785)	1,311,316	1,420,271	(567)	1,318,770
Balance (in shares) at Jun. 30, 2018	53,475,000	(28,920,000)
Balance at Mar. 31, 2018	$ 534	$ (1,397,962)	1,296,536	1,406,720	(699)	1,305,129
Balance (in shares) at Mar. 31, 2018	53,398,000	(28,771,000)
Increase (Decrease) in Stockholders' Equity
Stock compensation expense			10,439			10,439
Exercise of stock options	$ 1		4,341			4,342
Exercise of stock options (in shares)	79,000
Issuance of equity (in shares)	(2,000)
Repurchase of stock		$ (14,823)				(14,823)
Repurchase of stock (in shares)		(149,000)
Net income				13,551		13,551
Other comprehensive income (loss)-other					132	132
Balance at Jun. 30, 2018	$ 535	$ (1,412,785)	1,311,316	1,420,271	(567)	1,318,770
Balance (in shares) at Jun. 30, 2018	53,475,000	(28,920,000)
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					389,268
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
Adoption of new accounting standards | Accounting Standards Update 2016-02				(145)		(145)
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)
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	$ 1,433,348	$ 415	$ 1,334,270
Balance (in shares) at Jun. 30, 2019	54,063,000	(29,662,000)