Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	[1]	$ (12,468)		$ (20,939)	$ (54,595)
Other comprehensive income before reclassifications	[1]	10,115		8,818	(31,825)
Amounts reclassified from accumulated other comprehensive loss	[1]	(347)		(347)	65,481
Other comprehensive income (loss)	[1]	9,768		8,471	33,656
Ending balance	[1]	(2,700)		(12,468)	(20,939)
Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	[1]	0		(111)	(364)
Other comprehensive income before reclassifications	[1]			111	253
Amounts reclassified from accumulated other comprehensive loss	[1]			0	0
Other comprehensive income (loss)	[1]			111	253
Ending balance	[1]			0	(111)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	[1]	(11,002)		(12,041)	(4,709)
Other comprehensive income before reclassifications	[1]	3,286		1,039	(7,332)
Amounts reclassified from accumulated other comprehensive loss		0	[1]	0	0
Other comprehensive income (loss)	[1]	3,286		1,039	(7,332)
Ending balance	[1]	(7,716)		(11,002)	(12,041)
Investment in Convertible Preferred Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	[1]	0		126	126
Other comprehensive income before reclassifications	[1]	344		0	0
Amounts reclassified from accumulated other comprehensive loss	[1]	0		(126)	0
Other comprehensive income (loss)	[1]	344		(126)	0
Ending balance	[1]	344		0	126
Defined Benefit Plan Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	[1]	(1,466)		(8,913)	(49,648)
Other comprehensive income before reclassifications	[1]	6,485		7,668	(24,746)
Amounts reclassified from accumulated other comprehensive loss	[1]	(347)		(221)	65,481
Other comprehensive income (loss)	[1]	6,138		7,447	40,735
Ending balance	[1]	$ 4,672		$ (1,466)	$ (8,913)

[1] All amounts are net of tax. Amounts in parentheses indicate debits