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, 2018	$ 874,659	$ 677	$ (8,458)	$ 672,095	$ 210,345
Common stock issued beginning of period (shares) at Dec. 31, 2018		67,708
Treasury stock beginning of period (shares) at Dec. 31, 2018			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)	900		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		68,006
Treasury stock end of period (shares) at Mar. 31, 2019			1,472
Stockholders' equity beginning of period at Dec. 31, 2019	$ 981,512	$ 683	$ (26,616)	687,255	320,190
Common stock issued beginning of period (shares) at Dec. 31, 2019	68,300	68,306
Treasury stock beginning of period (shares) at Dec. 31, 2019	1,500		1,528
Stockholders' Equity [Abstract]
Exercise of stock options	$ 206	$ 0		206
Exercise of stock options (shares)		13
Shares vested for long-term incentive plan	0	$ 4		(4)
Shares vested for long-term incentive plan (shares)		402
Repurchases of common stock under share repurchase program	$ (1,416)		$ (1,416)
Repurchases of common stock under share repurchase program (shares)	100		87
Repurchases of common stock equity related to equity award activity	$ (2,441)		$ (2,441)
Repurchases of common stock related to equity award activity (shares)			122
Stock compensation expense	3,170			3,170
Net income	22,029				22,029
Stockholders' equity end of period at Mar. 31, 2020	$ 1,003,060	$ 687	$ (30,473)	$ 690,627	$ 342,219
Common stock issued end of period (shares) at Mar. 31, 2020	68,700	68,721
Treasury stock end of period (shares) at Mar. 31, 2020	1,700		1,737