Other Comprehensive Loss - Related Tax Effects Allocated to Each Component 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
Equity [Abstract]
Amortization of actuarial losses, before tax amount	$ 2,613	$ (763)	$ 1,808	$ (1,270)
Derivative instruments	(17)		322
Cumulative translation adjustment, before tax amount	233	(5,304)	338	(3,834)
Total other comprehensive income (loss), before tax amount	2,829	(6,067)	2,468	(5,104)
Amortization of actuarial losses, tax	(874)	170	(719)	338
Derivative instrument, tax	0		0
Cumulative translation adjustment, tax	0	0	0	0
Total other comprehensive income (loss), tax	(874)	170	(719)	338
Amortization of actuarial losses, after tax amount	1,739	(593)	1,089	(932)
Derivative instrument, after tax amount	(17)	0	322	0
Cumulative translation adjustment, after tax amount	233	(5,304)	338	(3,834)
Total other comprehensive income (loss)	$ 1,955	$ (5,897)	$ 1,749	$ (4,766)

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Amount before tax, after reclassification adjustments of other comprehensive income (loss).

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Amount before tax, after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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