Consolidated Statement of Changes in Retained Earnings and Accumulated Other Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 732,573
Net income	121,162	$ 137,649	$ 125,115
Pension and post-retirement plan adjustments, net of tax	9,296	(5,559)	(17,569)
(Income) loss attributable to noncontrolling interests	(1,220)	(1,136)	(660)
Balance at end of period	809,891	732,573
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,012,266	935,577	868,675
Net income	121,162	137,649	125,115
(Income) loss attributable to noncontrolling interests	(1,061)	(1,209)	(965)
Common dividends	(66,537)	(63,481)	(57,206)
Preferred dividends	(41)	(42)	(42)
Balance at end of period	1,065,789	1,012,266	935,577
Retained Earnings | Cumulative effect, period of adoption, adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period		3,772
Balance at end of period			3,772
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	(214,003)	(218,927)	(171,762)
Foreign currency translation adjustments	22,260	(1,657)	(30,103)
Pension and post-retirement plan adjustments, net of tax	9,296	(5,559)	(17,569)
Unrecognized net gains on available-for-sale securities (Note 18)	(7)	578	(572)
Reclassification of currency translation from accumulated other comprehensive (loss) into net income (Note 5)	216	15,261
(Income) loss attributable to noncontrolling interests	(159)	73	305
Balance at end of period	(182,397)	(214,003)	(218,927)
Accumulated Other Comprehensive Loss | Cumulative effect, period of adoption, adjustment
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period		(3,772)
Balance at end of period			(3,772)
Noncontrolling Interests
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	6,773	5,637	4,977
(Income) loss attributable to noncontrolling interests	1,220	1,136	660
Balance at end of period	$ 7,993	$ 6,773	$ 5,637