Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance (in shares) at Dec. 31, 2018		38,147
Beginning Balance at Dec. 31, 2018	$ 1,348,825	$ 381	$ 299,534	$ 1,196,727	$ (147,817)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	62,645			62,645
Other comprehensive income:
Cumulative translation adjustment	5,223				5,223
Issuance of common stock in connection with:
Exercise of options (in shares)		55
Exercise of options	2,212	$ 1	2,211
Restricted share grants, less net settled shares (in shares)		153
Restricted share grants, less net settled shares	(2,739)	$ 1	(2,740)
Stock units issued under incentive compensation plan	1,346		1,346
Purchase and retirement of common stock (in shares)		(328)
Purchase and retirement of common stock	(21,883)	$ (3)	(21,880)
Share-based compensation	6,393		6,393
Ending Balance (in shares) at Mar. 31, 2019		38,027
Ending Balance at Mar. 31, 2019	1,402,022	$ 380	284,864	1,259,372	(142,594)
Beginning Balance (in shares) at Dec. 31, 2018		38,147
Beginning Balance at Dec. 31, 2018	1,348,825	$ 381	299,534	1,196,727	(147,817)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	187,665
Other comprehensive income:
Cumulative translation adjustment	(16,225)
Issuance of common stock in connection with:
Stock units issued under incentive compensation plan	1,413
Ending Balance (in shares) at Sep. 30, 2019		37,629
Ending Balance at Sep. 30, 2019	1,461,234	$ 376	240,508	1,384,392	(164,042)
Beginning Balance (in shares) at Mar. 31, 2019		38,027
Beginning Balance at Mar. 31, 2019	1,402,022	$ 380	284,864	1,259,372	(142,594)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	64,598			64,598
Other comprehensive income:
Cumulative translation adjustment	(4,815)				(4,815)
Issuance of common stock in connection with:
Exercise of options (in shares)		87
Exercise of options	3,076	$ 1	3,075
Restricted share grants, less net settled shares (in shares)		78
Restricted share grants, less net settled shares	(1,351)	$ 1	(1,352)
Purchase and retirement of common stock (in shares)		(580)
Purchase and retirement of common stock	(48,332)	$ (6)	(48,326)
Share-based compensation	3,814		3,814
Ending Balance (in shares) at Jun. 30, 2019		37,612
Ending Balance at Jun. 30, 2019	1,419,012	$ 376	242,075	1,323,970	(147,409)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	60,422			60,422
Other comprehensive income:
Cumulative translation adjustment	(16,633)				(16,633)
Issuance of common stock in connection with:
Exercise of options (in shares)		94
Exercise of options	3,569	$ 1	3,568
Restricted share grants, less net settled shares (in shares)		14
Restricted share grants, less net settled shares	(1,322)	$ 0	(1,322)
Stock units issued under incentive compensation plan	67		67
Purchase and retirement of common stock (in shares)		(91)
Purchase and retirement of common stock	(7,734)	$ (1)	(7,733)
Share-based compensation	3,853		3,853
Ending Balance (in shares) at Sep. 30, 2019		37,629
Ending Balance at Sep. 30, 2019	$ 1,461,234	$ 376	240,508	1,384,392	(164,042)
Beginning Balance (in shares) at Dec. 31, 2019	37,390	37,390
Beginning Balance at Dec. 31, 2019	$ 1,489,142	$ 374	216,162	1,413,453	(140,847)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	56,747			56,747
Other comprehensive income:
Cumulative translation adjustment	(31,102)				(31,102)
Issuance of common stock in connection with:
Exercise of options (in shares)		34
Exercise of options	1,207	$ 1	1,206
Restricted share grants, less net settled shares (in shares)		136
Restricted share grants, less net settled shares	(6,767)	$ 1	(6,768)
Stock units issued under incentive compensation plan	2,314		2,314
Purchase and retirement of common stock (in shares)		(450)
Purchase and retirement of common stock	(50,311)	$ (5)	(50,306)
Share-based compensation	7,454		7,454
Ending Balance (in shares) at Mar. 31, 2020		37,110
Ending Balance at Mar. 31, 2020	$ 1,468,684	$ 371	170,062	1,470,200	(171,949)
Beginning Balance (in shares) at Dec. 31, 2019	37,390	37,390
Beginning Balance at Dec. 31, 2019	$ 1,489,142	$ 374	216,162	1,413,453	(140,847)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	155,093
Other comprehensive income:
Cumulative translation adjustment	(204)
Issuance of common stock in connection with:
Stock units issued under incentive compensation plan	2,314
Ending Balance (in shares) at Sep. 30, 2020		36,028
Ending Balance at Sep. 30, 2020	1,474,497	$ 360	46,642	1,568,546	(141,051)
Beginning Balance (in shares) at Mar. 31, 2020		37,110
Beginning Balance at Mar. 31, 2020	1,468,684	$ 371	170,062	1,470,200	(171,949)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	48,174			48,174
Other comprehensive income:
Cumulative translation adjustment	9,568				9,568
Issuance of common stock in connection with:
Exercise of options (in shares)		33
Exercise of options	1,191		1,191
Restricted share grants, less net settled shares (in shares)		38
Restricted share grants, less net settled shares	(2,154)	$ 1	(2,155)
Purchase and retirement of common stock (in shares)		(471)
Purchase and retirement of common stock	(51,053)	$ (5)	(51,048)
Share-based compensation	4,693		4,693
Ending Balance (in shares) at Jun. 30, 2020		36,710
Ending Balance at Jun. 30, 2020	1,479,103	$ 367	122,743	1,518,374	(162,381)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	50,172			50,172
Other comprehensive income:
Cumulative translation adjustment	21,330				21,330
Issuance of common stock in connection with:
Exercise of options (in shares)		43
Exercise of options	1,536		1,536
Restricted share grants, less net settled shares (in shares)		24
Restricted share grants, less net settled shares	(207)		(207)
Purchase and retirement of common stock (in shares)		(749)
Purchase and retirement of common stock	(82,866)	$ (7)	(82,859)
Share-based compensation	5,429		5,429
Ending Balance (in shares) at Sep. 30, 2020		36,028
Ending Balance at Sep. 30, 2020	$ 1,474,497	$ 360	$ 46,642	$ 1,568,546	$ (141,051)