CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common stock [Member]	Treasury stock [Member]	Additional paid-in capital [Member]	Retained earnings [Member]
Stockholders' equity, beginning of period at Dec. 31, 2016	$ 680,601	$ 668	$ (2,529)	$ 649,280	$ 33,182
Stockholders' Equity [Abstract]
Exercise of stock options	3,396	3		3,393
Shares vested for long-term incentive plan	0	2		(2)
Repurchases of common stock related to equity award activity	(1,292)		(1,292)
Stock compensation expense	6,769			6,769
Net income	57,425				57,425
Stockholders' equity, end of period at Dec. 31, 2017	746,899	$ 673	$ (3,821)	659,440	90,607
Common stock outstanding, beginning of period (in shares) at Dec. 31, 2016		66,814
Treasury shares, beginning of period (in shares) at Dec. 31, 2016			148
Stockholders Equity, Common Shares [Abstract]
Exercise of stock options (in shares)		260
Shares vested for long-term incentive plan		212
Repurchases of common stock related to equity award activity (in shares)			59
Common stock outstanding, end of period (in shares) at Dec. 31, 2017		67,286
Treasury shares, end of period (in shares) at Dec. 31, 2017			207
Stockholders' Equity [Abstract]
Exercise of stock options	1,327	$ 1		1,326
Shares vested for long-term incentive plan	0	3		(3)
Repurchases of common stock under share repurchase program	(2,891)		$ (2,891)
Repurchases of common stock related to equity award activity	(1,729)		(1,729)
Share withholdings made in satisfaction of exercise price	0		17	(17)
Stock compensation expense	11,315			11,315
Net income	119,738				119,738
Stockholders' equity, end of period at Dec. 31, 2018	$ 874,659	$ 677	$ (8,458)	672,095	210,345
Stockholders Equity, Common Shares [Abstract]
Exercise of stock options (in shares)		96
Shares vested for long-term incentive plan		326
Repurchases of common stock under share repurchase program (in shares)			182
Repurchases of common stock related to equity award activity (in shares)			88
Share withholdings made in satisfaction of exercise price (shares)			1
Common stock outstanding, end of period (in shares) at Dec. 31, 2018	67,200	67,708
Treasury shares, end of period (in shares) at Dec. 31, 2018	500		478
Stockholders' Equity [Abstract]
Exercise of stock options	$ 2,704	$ 2		2,702
Shares vested for long-term incentive plan	0	4		(4)
Repurchases of common stock under share repurchase program	(16,446)		$ (16,446)
Repurchases of common stock related to equity award activity	(1,712)		(1,712)
Stock compensation expense	12,462			12,462
Net income	109,845				109,845
Stockholders' equity, end of period at Dec. 31, 2019	$ 981,512	$ 683	$ (26,616)	$ 687,255	$ 320,190
Stockholders Equity, Common Shares [Abstract]
Exercise of stock options (in shares)		199
Shares vested for long-term incentive plan		399
Repurchases of common stock under share repurchase program (in shares)			961
Repurchases of common stock related to equity award activity (in shares)			89
Common stock outstanding, end of period (in shares) at Dec. 31, 2019	66,800	68,306
Treasury shares, end of period (in shares) at Dec. 31, 2019	1,500		1,528