Accumulated Other Comprehensive Loss (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period			$ 848,324
Other comprehensive income (loss)	$ 1,467	$ (14,930)	(3,122)	$ (7,109)
Balance, end of period	897,514	804,785	897,514	804,785
AOCI, pension and other postretirement benefit plans, tax benefits (expense)	9,893	9,536	9,893	9,536	$ 9,984	$ 9,563
AOCI, cumulative changes in net gain (loss) from cash flow hedges, tax benefit (expense)	278	(316)	278	(316)	$ (106)	$ (15)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period			(30,488)	(17,983)
Other comprehensive income (loss) before reclassifications			(2,075)	(8,293)
Amounts reclassified from accumulated other comprehensive loss			0	0
Other comprehensive income (loss)			(2,075)	(8,293)
Balance, end of period	(32,563)	(26,276)	(32,563)	(26,276)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period			(48,700)	(47,198)
Other comprehensive income (loss) before reclassifications			0	0
Amounts reclassified from accumulated other comprehensive loss			313	87
Other comprehensive income (loss)			313	87
Balance, end of period	(48,387)	(47,111)	(48,387)	(47,111)
Derivative Instrument Designated as Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period			354	26
Other comprehensive income (loss) before reclassifications			(1,204)	1,153
Amounts reclassified from accumulated other comprehensive loss			(156)	(56)
Other comprehensive income (loss)			(1,360)	1,097
Balance, end of period	(1,006)	1,123	(1,006)	1,123
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance, beginning of period	(83,423)	(57,334)	(78,834)	(65,155)
Other comprehensive income (loss) before reclassifications			(3,279)	(7,140)
Amounts reclassified from accumulated other comprehensive loss			157	31
Other comprehensive income (loss)	1,467	(14,930)	(3,122)	(7,109)
Balance, end of period	$ (81,956)	$ (72,264)	$ (81,956)	$ (72,264)