CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Shares	Retained Earnings	Accumulated Other Comprehensive Income/(Loss)	Non-controlling Interest
Beginning balance (in shares) at Dec. 31, 2015		122,770,217
Beginning balance at Dec. 31, 2015	$ 1,361,740	$ 708,827	$ 612,760	$ (33,503)	$ 73,656
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	217,770		211,972		5,798
Dividends ($1.00 and $0.75 per share, respectively)	(123,155)		(123,155)
Issuance of shares under incentive stock plans (in shares)		179,743
Issuance of shares under incentive stock plans	1,576	$ 1,576
Stock-based compensation	5,136	$ 5,136
Repurchase of common shares (in shares)		(45,592)
Repurchase of common shares	(868)	$ (178)	(690)
Actuarial change and amortization of pension and postretirement plan liabilities	5,533			5,533
Foreign currency translation adjustment	6,322			2,780	3,542
Cash flow hedges	22,822			22,608	214
Recapitalization of New Zealand Joint Venture	0	(5,398)		3,438	1,960
Recapitalization costs	(124)	$ (96)			(28)
Ending balance (in shares) at Dec. 31, 2016		122,904,368
Ending balance at Dec. 31, 2016	1,496,752	$ 709,867	700,887	856	85,142
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)
Net income	94,659		84,691		9,968
Dividends ($1.00 and $0.75 per share, respectively)	(95,302)		(95,302)
Issuance of shares under incentive stock plans (in shares)		262,561
Issuance of shares under incentive stock plans	3,665	$ 3,665
Stock-based compensation	4,084	$ 4,084
Repurchase of common shares (in shares)		(298)
Repurchase of common shares	0
Actuarial change and amortization of pension and postretirement plan liabilities	349			349
Foreign currency translation adjustment	16,599			13,335	3,264
Cash flow hedges	(1,597)			(1,902)	305
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 Sep. 30, 2017		128,916,631
Ending balance at Sep. 30, 2017	$ 1,657,234	$ 870,006	$ 675,911	$ 12,638	$ 98,679