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 | 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 $0.79 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]
Cumulative-effect adjustment due to adoption of ASU | Accounting Standards Update 2018-02	0		711	(711)
Net income	112,682		100,229		12,453
Dividends ($1.00 and $0.79 per share, respectively)	(102,787)		(102,787)
Issuance of shares under incentive stock plans (in shares)		577,857
Issuance of shares under incentive stock plans	8,216	$ 8,216
Stock-based compensation	4,957	$ 4,957
Repurchase of common shares (in shares)		(81,396)
Repurchase of common shares	(2,980)	$ (2,980)
Amortization of pension and postretirement plan liabilities	(507)			(507)
Actuarial change and amortization of pension and postretirement plan liabilities	(204)
Foreign currency translation adjustment	(30,599)			(23,341)	(7,258)
Cash flow hedges	21,285			22,476	(1,191)
Dividend to New Zealand minority shareholder	(3,122)				(3,122)
Ending balance (in shares) at Sep. 30, 2018		129,467,237
Ending balance at Sep. 30, 2018	$ 1,701,099	$ 882,421	$ 705,531	12,348	$ 100,799
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment due to adoption of ASU | Accounting Standards Update 2018-02				$ 700