CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Shares	Retained Earnings	Accumulated Other Comprehensive Income	Non-controlling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment due to adoption of ASU No. 2016-16 | Accounting Standards Update 2016-16	$ (14,365)		$ (14,365)
Beginning balance (in shares) at Dec. 31, 2016		122,904,368
Beginning balance at Dec. 31, 2016	1,496,752	$ 709,867	700,887	$ 856	$ 85,142
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	161,579		148,842		12,737
Dividends ($1.00 and $0.52 per share, respectively)	(127,986)		(127,986)
Issuance of shares under incentive stock plans (in shares)		322,314
Issuance of shares under incentive stock plans	4,751	$ 4,751
Stock-based compensation	5,396	$ 5,396
Repurchase of common shares (in shares)		(5,906)
Repurchase of common shares	(176)	$ (176)
Actuarial change and amortization of pension and postretirement plan liabilities	(208)			(208)
Foreign currency translation adjustment	9,114			7,416	1,698
Cash flow hedges	5,693			5,353	340
Issuance of shares under equity offering, net of costs (in shares)		5,750,000
Issuance of shares under equity offering, net of costs	152,390	$ 152,390
Ending balance (in shares) at Dec. 31, 2017		128,970,776
Ending balance at Dec. 31, 2017	1,692,940	$ 872,228	707,378	13,417	99,917
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	82,043		76,797		5,246
Dividends ($1.00 and $0.52 per share, respectively)	(67,847)		(67,847)
Issuance of shares under incentive stock plans (in shares)		561,475
Issuance of shares under incentive stock plans	7,824	$ 7,824
Stock-based compensation	3,474	$ 3,474
Repurchase of common shares (in shares)		(80,983)
Repurchase of common shares	(2,966)	$ (2,966)
Actuarial change and amortization of pension and postretirement plan liabilities	338			338
Foreign currency translation adjustment	(20,072)			(15,251)	(4,821)
Cash flow hedges	17,143			18,097	(954)
Ending balance (in shares) at Jun. 30, 2018		129,451,268
Ending balance at Jun. 30, 2018	$ 1,712,877	$ 880,560	$ 716,328	$ 16,601	$ 99,388