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, 2017	$ 746,899	$ 673	$ (3,821)	$ 659,440	$ 90,607
Common stock issued beginning of period (shares) at Dec. 31, 2017		67,286
Treasury stock beginning of period (shares) at Dec. 31, 2017			207
Stockholders' Equity [Abstract]
Exercise of stock options	588	$ 1		587
Exercise of stock options (shares)		55
Shares vested for long-term incentive plan	0	$ 1		(1)
Shares vested for long-term incentive plan (shares)		155
Repurchases of common stock equity related to equity award activity	(1,046)		$ (1,046)
Repurchases of common stock related to equity award activity (shares)			53
Share withholdings made in satisfaction of exercise price	0		$ (17)	17
Share withholdings made in satisfaction of exercise price (shares)			1
Stock compensation expense	1,775			1,775
Net income	15,359				15,359
Stockholders' equity end of period at Mar. 31, 2018	763,575	$ 675	$ (4,884)	661,818	105,966
Common stock issued end of period (shares) at Mar. 31, 2018		67,496
Treasury stock end of period (shares) at Mar. 31, 2018			261
Stockholders' equity beginning of period at Dec. 31, 2018	$ 874,659	$ 677	$ (8,458)	672,095	210,345
Common stock issued beginning of period (shares) at Dec. 31, 2018	67,700	67,708
Treasury stock beginning of period (shares) at Dec. 31, 2018	500		478
Stockholders' Equity [Abstract]
Exercise of stock options	$ 132	$ 0		132
Exercise of stock options (shares)		8
Shares vested for long-term incentive plan	0	$ 3		(3)
Shares vested for long-term incentive plan (shares)		290
Repurchases of common stock under share repurchase program	(15,709)		$ (15,709)
Repurchases of common stock under share repurchase program (shares)			920
Repurchases of common stock equity related to equity award activity	(1,330)		$ (1,330)
Repurchases of common stock related to equity award activity (shares)			74
Stock compensation expense	2,915			2,915
Net income	20,350				20,350
Stockholders' equity end of period at Mar. 31, 2019	$ 881,017	$ 680	$ (25,497)	$ 675,139	$ 230,695
Common stock issued end of period (shares) at Mar. 31, 2019	68,000	68,006
Treasury stock end of period (shares) at Mar. 31, 2019	1,500		1,472