CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock and Additional Paid-In Capital	Retained Earnings	Cumulative Translation Adjustment	Retirement Benefits Adjustments	Cumulative Unrealized Gain (Loss) on Derivatives	Treasury Stock
Balance at Dec. 31, 2014	$ 1,486,451	$ 648,451	$ 1,483,821	$ (24,813)	$ (40,316)	$ (27,149)	$ (553,543)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	282,807		282,807
Cumulative translation adjustment	(68,166)			(68,166)
Net change in retirement obligations, net of tax	9,415				9,415
Net change on derivatives designated as cash flow hedges, net of tax	4,531					4,531
Issuance of shares of common stock from issuance of unvested shares, exercise of stock options and deferred compensation plans	24,482	14,545					9,937
Repurchase of common stock	(210,551)						(210,551)
Share-based compensation	17,529	17,529
Unvested shares surrendered for tax withholding	(3,259)						(3,259)
Cash dividends declared	(99,948)		(99,948)
Balance at Dec. 31, 2015	1,443,291	680,525	1,666,680	(92,979)	(30,901)	(22,618)	(757,416)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	271,109		271,109
Cumulative translation adjustment	(62,565)			(62,565)
Net change in retirement obligations, net of tax	3,049				3,049
Net change on derivatives designated as cash flow hedges, net of tax	4,361					4,361
Issuance of shares of common stock from issuance of unvested shares, exercise of stock options and deferred compensation plans	30,240	253					29,987
Repurchase of common stock	(54,950)						(54,950)
Share-based compensation	17,337	17,337
Unvested shares surrendered for tax withholding	(4,928)						(4,928)
Cash dividends declared	(103,050)		(103,050)
Balance at Dec. 31, 2016	1,543,894	698,115	1,834,739	(155,544)	(27,852)	(18,257)	(787,307)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	337,257		337,257
Cumulative translation adjustment	113,170			113,170
Net change in retirement obligations, net of tax	(1,302)				(1,302)
Net change on derivatives designated as cash flow hedges, net of tax	4,210					4,210
Issuance of shares of common stock from issuance of unvested shares, exercise of stock options and deferred compensation plans	22,935						22,935
Repurchase of common stock	(29,074)						(29,074)
Share-based compensation	19,693	19,693
Unvested shares surrendered for tax withholding	(6,228)						(6,228)
Tax effect of reversal of indefinite assertion on certain intercompany loans	(3,932)			(3,932)
Cash dividends declared	(114,081)		(114,081)
Balance at Dec. 31, 2017	$ 1,886,542	$ 717,808	$ 2,057,915	$ (46,306)	$ (29,154)	$ (14,047)	$ (799,674)