CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Treasury Stock [Member]	Noncontrolling Interests
Beginning balance at Dec. 31, 2017	$ 932,453	$ 9,858	$ 334,309	$ 2,388,219	$ (247,186)	$ (1,553,563)	$ 816
Beginning Balance (in shares) at Dec. 31, 2017		65,663,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income including non-controlling interests	60,820			60,824			(4)
Unrecognized amounts from defined benefit pension plans, net of tax	1,287				1,287
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax	855				855
Currency translation adjustment	19,387				19,328		59
Cash dividends declared - $0.47 per share and $0.39 per share in 2019 and 2018, respectively	(25,787)			(25,787)
Stock-based compensation activity		55,000
Issuance of shares under benefit plans	6,381		5,819			562
Purchase of treasury shares	(14,724)					(14,724)
Purchase of shares for treasury (in shares)		(159,000)
Stockholders' Equity, Other	0		5,483	(5,483)
Ending balance at Mar. 31, 2018	980,672	$ 9,858	345,611	2,417,773	(225,716)	(1,567,725)	871
Ending Balance (in shares) at Mar. 31, 2018		65,559,000
Beginning balance at Dec. 31, 2017	932,453	$ 9,858	334,309	2,388,219	(247,186)	(1,553,563)	816
Beginning Balance (in shares) at Dec. 31, 2017		65,663,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income including non-controlling interests	129,679
Unrecognized amounts from defined benefit pension plans, net of tax	2,008
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax	(377)
Currency translation adjustment	(30,955)
Ending balance at Jun. 30, 2018	943,508	$ 9,858	351,632	2,461,130	(276,479)	(1,603,409)	776
Ending Balance (in shares) at Jun. 30, 2018		65,172,000
Beginning balance at Mar. 31, 2018	980,672	$ 9,858	345,611	2,417,773	(225,716)	(1,567,725)	871
Beginning Balance (in shares) at Mar. 31, 2018		65,559,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income including non-controlling interests	68,859			68,864			(5)
Unrecognized amounts from defined benefit pension plans, net of tax	721				721
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax	(1,232)				(1,232)
Currency translation adjustment	(50,342)				(50,252)		(90)
Cash dividends declared - $0.47 per share and $0.39 per share in 2019 and 2018, respectively	(25,701)			(25,701)
Stock-based compensation activity		15,000
Issuance of shares under benefit plans	6,039		6,215			(176)
Purchase of treasury shares	(35,508)					(35,508)
Purchase of shares for treasury (in shares)		(402,000)
Stockholders' Equity, Other	0		(194)	194
Ending balance at Jun. 30, 2018	943,508	$ 9,858	351,632	2,461,130	(276,479)	(1,603,409)	776
Ending Balance (in shares) at Jun. 30, 2018		65,172,000
Beginning balance at Dec. 31, 2018	887,592	$ 9,858	360,308	2,564,440	(293,739)	(1,753,925)	650
Beginning Balance (in shares) at Dec. 31, 2018		63,546,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income including non-controlling interests	71,466			71,480			(14)
Unrecognized amounts from defined benefit pension plans, net of tax	787				787
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax	329				329
Currency translation adjustment	5,136				5,099		37
Cash dividends declared - $0.47 per share and $0.39 per share in 2019 and 2018, respectively	(29,847)			(29,847)
Stock-based compensation activity		148,000
Issuance of shares under benefit plans	4,786		3,302			1,484
Purchase of treasury shares	(75,584)					(75,584)
Purchase of shares for treasury (in shares)		(894,000)
Stockholders' Equity, Other	0		808	(808)
Ending balance at Mar. 31, 2019	864,665	$ 9,858	364,418	2,605,265	(287,524)	(1,828,025)	673
Ending Balance (in shares) at Mar. 31, 2019		62,800,000
Beginning balance at Dec. 31, 2018	887,592	$ 9,858	360,308	2,564,440	(293,739)	(1,753,925)	650
Beginning Balance (in shares) at Dec. 31, 2018		63,546,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income including non-controlling interests	156,910
Unrecognized amounts from defined benefit pension plans, net of tax	1,878
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax	28
Currency translation adjustment	$ 9,985
Purchase of shares for treasury (in shares)	(1,900,000)
Ending balance at Jun. 30, 2019	$ 846,058	$ 9,858	368,919	2,661,720	(281,850)	(1,913,219)	630
Ending Balance (in shares) at Jun. 30, 2019		61,779,000
Beginning balance at Mar. 31, 2019	864,665	$ 9,858	364,418	2,605,265	(287,524)	(1,828,025)	673
Beginning Balance (in shares) at Mar. 31, 2019		62,800,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income including non-controlling interests	85,444			85,452			(8)
Unrecognized amounts from defined benefit pension plans, net of tax	1,091				1,091
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax	(301)				(301)
Currency translation adjustment	4,849				4,884		(35)
Cash dividends declared - $0.47 per share and $0.39 per share in 2019 and 2018, respectively	(29,279)			(29,279)
Stock-based compensation activity		13,000
Issuance of shares under benefit plans	4,919		4,783			136
Purchase of treasury shares	$ (85,330)					(85,330)
Purchase of shares for treasury (in shares)	(1,000,000.0)	(1,034,000)
Stockholders' Equity, Other	$ 0		(282)	282
Ending balance at Jun. 30, 2019	$ 846,058	$ 9,858	$ 368,919	$ 2,661,720	$ (281,850)	$ (1,913,219)	$ 630
Ending Balance (in shares) at Jun. 30, 2019		61,779,000