Condensed Consolidated Statements of Stockholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock Shares [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 6,330					$ 6,330
Common stock, shares outstanding at Dec. 31, 2017		20,210,000
Stockholders' Equity Attributable to Parent at Dec. 31, 2017	1,198,254		$ 2,021	$ 625,568	$ 0	585,624	$ (14,959)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		130,000
Stock Issued During Period, Value, New Issues	3,155		11	982	2,162
Shares Paid for Tax Withholding for Share Based Compensation		(23,000)
Adjustments Related to Tax Withholding for Share-based Compensation	(5,338)				(5,338)
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	5,462			5,462
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	17,213						17,213
Net Income (Loss) Attributable to Parent	4,875					4,875
Stockholders' Equity Attributable to Parent at Mar. 31, 2018	$ 1,229,951		2,032	632,012	(3,176)	596,829	2,254
Common stock, shares outstanding at Mar. 31, 2018		20,317,000
Common stock, shares outstanding at Dec. 31, 2018	20,491,000	20,492,000
Stockholders' Equity Attributable to Parent at Dec. 31, 2018	$ 1,263,655		2,049	657,899	(95)	620,747	(16,945)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		254,000
Stock Issued During Period, Value, New Issues	$ 925		18	(4,289)	5,196
Shares Paid for Tax Withholding for Share Based Compensation	(77,642)	(78,000)
Adjustments Related to Tax Withholding for Share-based Compensation	$ (18,157)				(18,157)
Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition	6,209			6,209
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	(936)						(936)
Net Income (Loss) Attributable to Parent	30,998					30,998
Stockholders' Equity Attributable to Parent at Mar. 31, 2019	$ 1,282,694		$ 2,067	$ 659,819	$ (13,056)	$ 651,745	$ (17,881)
Common stock, shares outstanding at Mar. 31, 2019	20,612,000	20,668,000