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
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation		(23,000)
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(5,338)				(5,338)
APIC, Share-based Payment Arrangement, Increase for Cost 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		143,000
Stock Issued During Period, Value, New Issues	9,382		14	6,080	3,288
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation		0
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(132)				(132)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	6,297			6,297
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	(19,484)						(19,484)
Net Income (Loss) Attributable to Parent	31,054					31,054
Stockholders' Equity Attributable to Parent at Jun. 30, 2018	1,257,068		2,046	644,389	(20)	627,883	(17,230)
Common stock, shares outstanding at Jun. 30, 2018		20,460,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		31,000
Stock Issued During Period, Value, New Issues	1,674		3	1,130	541
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation		(2,000)
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(649)				(649)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	6,233			6,233
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	(4,231)						(4,231)
Net Income (Loss) Attributable to Parent	219					219
Stockholders' Equity Attributable to Parent at Sep. 30, 2018	$ 1,260,314		2,049	651,752	(128)	628,102	(21,461)
Common stock, shares outstanding at Sep. 30, 2018		20,489,000
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		5,196
Adjustments to Additional Paid in Capital, Other				(4,289)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation		(78,000)
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(18,157)				(18,157)
APIC, Share-based Payment Arrangement, Increase for Cost 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		20,668,000
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 Payment Arrangement, Shares Withheld for Tax Withholding Obligation	(79,313)
Stockholders' Equity Attributable to Parent at Sep. 30, 2019	$ 1,340,335		2,067	659,709	0	701,141	(22,582)
Common stock, shares outstanding at Sep. 30, 2019	20,671,000	20,671,000
Common stock, shares outstanding at Mar. 31, 2019		20,668,000
Stockholders' Equity Attributable to Parent at Mar. 31, 2019	$ 1,282,694		2,067	659,819	(13,056)	651,745	(17,881)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		0
Stock Issued During Period, Value, New Issues	3,009		0		11,514
Adjustments to Additional Paid in Capital, Other				(8,505)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation		0
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(108)				(108)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	6,229			6,229
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	3,207						3,207
Net Income (Loss) Attributable to Parent	22,833					22,833
Stockholders' Equity Attributable to Parent at Jun. 30, 2019	1,317,864		2,067	657,543	(1,650)	674,578	(14,674)
Common stock, shares outstanding at Jun. 30, 2019		20,668,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		4,000
Stock Issued During Period, Value, New Issues	307		0		1,863
Adjustments to Additional Paid in Capital, Other				(1,556)
Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation		(1,000)
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	(213)				(213)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	3,722			3,722
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	(7,908)						(7,908)
Net Income (Loss) Attributable to Parent	26,563					26,563
Stockholders' Equity Attributable to Parent at Sep. 30, 2019	$ 1,340,335		$ 2,067	$ 659,709	$ 0	$ 701,141	$ (22,582)
Common stock, shares outstanding at Sep. 30, 2019	20,671,000	20,671,000