Condensed Consolidated Statements of Changes in Retained Earnings, Accumulated Other Comprehensive Loss and Noncontrolling Interests - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 801,898
Net income	$ 25,125	$ 36,066	61,539	$ 79,741
Pension and post-retirement plan adjustments, net of tax	3,657	3,090	7,369	6,192
Income attributable to noncontrolling interests	(262)	(340)	(448)	(468)
Preferred dividends	(10)	(10)	(20)	(20)
Ending balance	840,419		840,419
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	1,085,383	1,039,609	1,065,789	1,012,266
Net income	25,387	36,406	61,987	80,209
Income attributable to noncontrolling interests	(262)	(340)	(448)	(468)
Common dividends	(17,237)	(16,710)	(34,047)	(33,032)
Preferred dividends	(10)	(10)	(20)	(20)
Ending balance	1,093,261	1,058,955	1,093,261	1,058,955
Accumulated Other Comprehensive (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(188,948)	(233,075)	(182,397)	(214,003)
Foreign currency translation adjustments	6,018	4,669	(4,205)	(18,278)
Pension and post-retirement plan adjustments, net of tax	3,657	3,090	7,369	6,192
Unrealized net gains (losses) on available-for-sale securities	1	124	(4)	62
Reclassification from accumulated other comprehensive (loss) into net income (Note 5)				720
Income attributable to noncontrolling interests	127	(18)	92	97
Ending balance	(179,145)	(225,210)	(179,145)	(225,210)
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	8,214	6,786	7,993	6,773
Income attributable to noncontrolling interests	135	358	356	371
Ending balance	$ 8,349	$ 7,144	$ 8,349	$ 7,144