Consolidated Statement of Changes in Retained Earnings and Accumulated Other Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance			$ 597,601
Net income	$ 34,063	$ 32,226	99,973	$ 59,530
Pension and post-retirement plan actuarial gains, net of tax (Note 7)	2,651	2,180	8,039	6,321
(Income) loss attributable to noncontrolling interests	(346)	(160)	(706)	(519)
Income attributable to noncontrolling interests	(152)	(4,289)	(409)	(3,185)
Preferred dividends	(10)	(10)	(30)	(30)
Ending Balance	654,320		654,320
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	906,244	896,621	868,675	901,415
Net income	34,063	32,226	99,973	59,530
(Income) loss attributable to noncontrolling interests	(346)	(160)	(706)	(519)
Common dividends	(14,614)	(13,366)	(42,575)	(39,170)
Preferred dividends	(10)	(10)	(30)	(30)
Ending Balance	925,337	915,311	925,337	915,311
Accumulated Other Comprehensive (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(181,525)	(199,775)	(171,762)	(230,246)
Foreign currency translation adjustments	(4,755)	10,021	(19,235)	34,888
Pension and post-retirement plan actuarial gains, net of tax (Note 7)	2,651	2,180	8,039	6,321
Reclassification from accumulated other comprehensive loss into net income			(774)
Income attributable to noncontrolling interests	194	(4,129)	297	(2,666)
Ending Balance	$ (183,435)	(191,703)	$ (183,435)	(191,703)
Accounting Standards Update 2016-16
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of the adoption of ASU 2016-16 (Note 2)		$ (5,915)		$ (5,915)