Accumulated Other Comprehensive (Loss) Income - Summary of components of accumulated other comprehensive (loss) income (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		$ (18,102)	$ (17,969)
Change during the period
Before-tax amount		1,129	(1,382)
Tax (expense) benefit		(269)	742
Reclassification adjustment, net of taxes:
Realized loss on securities		0	0
Amortization of net loss	[1]	540	507
Total activity in period		1,400	(133)
Balance		(16,702)	(18,102)
Pension Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		(15,503)	(14,715)
Change during the period
Before-tax amount		776	(2,039)
Tax (expense) benefit		(283)	744
Reclassification adjustment, net of taxes:
Realized loss on securities		0	0
Amortization of net loss	[1]	540	507
Total activity in period		1,033	(788)
Balance		(14,470)	(15,503)
Unrealized Gain (Loss) On Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		39	36
Change during the period
Before-tax amount		(38)	5
Tax (expense) benefit		14	(2)
Reclassification adjustment, net of taxes:
Realized loss on securities		0	0
Amortization of net loss	[1]	0	0
Total activity in period		(24)	3
Balance		15	39
Foreign Currency Translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance		(2,638)	(3,290)
Change during the period
Before-tax amount		391	652
Tax (expense) benefit		0	0
Reclassification adjustment, net of taxes:
Realized loss on securities		0	0
Amortization of net loss	[1]	0	0
Total activity in period		391	652
Balance		$ (2,247)	$ (2,638)

[1] Reported as part of selling, general and administrative expenses.