Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Beginning Balance at Dec. 31, 2017	$ 523	$ (100,694)	$ 232,670	$ (724)	$ 854,176	$ 985,951
Beginning Balance, Shares at Dec. 31, 2017	52,277	4,152
Comprehensive income				228	153,480	153,708
Adoption impact - ASU 2018-02				(156)	156
Common stock purchased for treasury		$ (4,135)				(4,135)
Common stock purchased for treasury, shares		39
Restricted shares forfeited, Shares		94
Share-based compensation	$ 2	$ (15,153)	17,064			1,913
Share-based compensation, Shares	163	151
Exercise of stock options	$ 1		2,094			2,095
Exercise of stock options, Shares	130
Ending Balance at Sep. 30, 2018	$ 526	$ (119,982)	251,828	(652)	1,006,638	1,138,358
Ending Balance, Shares at Sep. 30, 2018	52,570	4,436
Cumulative effect from the adoption of accounting pronouncements, net of taxes					(1,174)	(1,174)
Beginning Balance at Dec. 31, 2018	$ 527	$ (125,452)	256,806	(453)	1,082,169	1,213,597
Beginning Balance, Shares at Dec. 31, 2018	52,690	4,489
Comprehensive income				(329)	182,506	182,177
Common stock purchased for treasury		$ (17,293)				(17,293)
Common stock purchased for treasury, shares		175
Restricted shares forfeited, Shares		15
Share-based compensation	$ 1	$ (8,127)	7,739			(387)
Share-based compensation, Shares	152	68
Exercise of stock options	$ 2		3,734			3,736
Exercise of stock options, Shares	208
Ending Balance at Sep. 30, 2019	$ 530	$ (150,872)	$ 268,279	$ (782)	$ 1,264,675	$ 1,381,830
Ending Balance, Shares at Sep. 30, 2019	53,050	4,747