Other Comprehensive Income (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]
Balance, at beginning of year	$ (24,400)		$ (11,300)
Net unrealized gains (losses) arising during the period	3,300		(15,040)
Less: Net realized gains reclassified to net income	(3,770)		(1,940)
Other Comprehensive Income (Loss)	7,070		(13,100)		$ (13,210)
Balance, at end of year	(17,330)		(24,400)		(11,300)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax	1,670		250		1,810
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	(650)		(730)		(2,650)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	6,050		(12,620)		(12,370)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, Tax	300		300
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	1,300		700
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax	300		700
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	1,900		300
Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, at beginning of year	(12,120)		(12,370)
Net unrealized gains (losses) arising during the period	1,000	[1]	(1,270)	[2]
Less: Net realized gains reclassified to net income	(670)	[3]	(1,520)	[4]
Balance, at end of year	(10,450)		(12,120)		(12,370)
Derivative Instruments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, at beginning of year	(2,520)		(1,790)
Net unrealized gains (losses) arising during the period	(3,750)	[1]	(1,150)	[2]
Less: Net realized gains reclassified to net income	(3,100)	[3]	(420)	[4]
Balance, at end of year	(3,170)		(2,520)		(1,790)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, at beginning of year	(9,760)		2,860
Net unrealized gains (losses) arising during the period	6,050		(12,620)
Less: Net realized gains reclassified to net income	0		0
Balance, at end of year	$ (3,710)		$ (9,760)		$ 2,860

[1] Defined benefit plans, net of income tax of $0.3 million. See Note 15, "Employee Benefit Plans," for additional details. Derivative instruments, net of income tax of $1.3 million. See Note 12, "Derivative Instruments," for further details.

[2] Defined benefit plans, net of income tax of $0.3 million. See Note 15, "Employee Benefit Plans," for additional details. Derivative instruments, net of income tax expense of $0.7 million. See Note 12, "Derivative Instruments," for further details.

[3] Defined benefit plans, net of income tax of $0.3 million. See Note 15, "Employee Benefit Plans," for additional details. Derivative instruments, net of income tax of $1.9 million. See Note 12, "Derivative Instruments," for further details

[4] Defined benefit plans, net of income tax of $0.7 million. See Note 15, "Employee Benefit Plans," for additional details. Derivative instruments, net of income tax expense of $0.3 million. See Note 12, "Derivative Instruments," for further details.