Consolidated Statement of Changes in Retained Earnings and Accumulated Other Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 517,128
Net income	93,862	$ 67,944	$ 87,927
Pension and post-retirement plan adjustments, net of tax	1,321	6,181	(48,490)
Loss (gain) attributable to noncontrolling interests	(3,578)	4,280	1,176
Balance at end of period	561,212	517,128
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	858,553	835,126	792,206
Net income	93,862	67,944	87,927
Foreign currency translation adjustments	0	0	0
Pension and post-retirement plan adjustments, net of tax	0	0	0
Reclassification from accumulated other comprehensive (loss) into net income	0
Loss (gain) attributable to noncontrolling interests	(1,926)	2,863	579
Common dividends	(49,032)	(47,338)	(45,544)
Preferred dividends	(42)	(42)	(42)
Balance at end of period	901,415	858,553	835,126
Accumulated Other Comprehensive (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	(208,199)	(166,730)	(78,269)
Net income	0	0	0
Foreign currency translation adjustments	(24,986)	(49,067)	(40,568)
Pension and post-retirement plan adjustments, net of tax	1,321	6,181	(48,490)
Reclassification from accumulated other comprehensive (loss) into net income	3,270
Loss (gain) attributable to noncontrolling interests	(1,652)	1,417	597
Common dividends	0	0	0
Preferred dividends	0	0	0
Balance at end of period	$ (230,246)	$ (208,199)	$ (166,730)