Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI before tax, beginning balance	$ (7,289)	$ (5,539)	$ (5,336)	$ (6,945)	$ (8,079)	$ (8,801)	$ (5,336)	$ (8,801)
Accumulated other comprehensive income, tax, beginning balance	(949)	(960)	(970)	(1,047)	(1,063)	(1,080)	(970)	(1,080)
Accumulated Other Comprehensive Income Beginning Balance	(6,340)	(4,579)	(4,366)	(5,898)	(7,016)	(7,721)	(4,366)	(7,721)
Cumulative effect of new accounting principle in period of adoption									$ 274	$ 0
Other comprehensive income (loss), net of tax	166			1,608			(1,808)	3,431
AOCI before tax, ending balance	(7,113)	(7,289)	(5,539)	(5,321)	(6,945)	(8,079)	(7,113)	(5,321)
Accumulated other comprehensive income, tax, ending balance	(939)	(949)	(960)	(1,031)	(1,047)	(1,063)	(939)	(1,031)
Accumulated Other Comprehensive Income Ending Balance	(6,174)	(6,340)	(4,579)	(4,290)	(5,898)	(7,016)	(6,174)	(4,290)
Accumulated Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI before tax, beginning balance	(4,375)	(2,588)	(2,698)	(4,078)	(5,169)	(5,848)	(2,698)	(5,848)
Other comprehensive income adjustments	139	(1,787)	110	1,581	1,091	679
Other comprehensive income (loss), net of tax	139	(1,787)	110	1,581	1,091	679
AOCI before tax, ending balance	(4,236)	(4,375)	(2,588)	(2,497)	(4,078)	(5,169)	(4,236)	(2,497)
Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income adjustments	37	37	37	43	43	43
Other comprehensive income (loss), tax	10	11	10	16	16	17
Other comprehensive income (loss), net of tax	27	26	27	27	27	26
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption									(350)	$ 0
Minimum Pension Liability Adjustment | Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI before tax, beginning balance	172	179	171	188	192	197	171	197
Other comprehensive income adjustments	(7)	(7)	(7)	(4)	(4)	(5)
AOCI before tax, ending balance	165	172	179	184	188	192	165	184
Postretirement Health Coverage | Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI before tax, beginning balance	(3,086)	(3,130)	(2,809)	(3,055)	(3,102)	(3,150)	(2,809)	(3,150)
Other comprehensive income adjustments	44	44	44	47	47	48
AOCI before tax, ending balance	$ (3,042)	$ (3,086)	$ (3,130)	$ (3,008)	$ (3,055)	$ (3,102)	$ (3,042)	$ (3,008)
Accounting Standards Update 2014-09
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption									(350)
Accounting Standards Update 2014-09 | Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption									(350)
Accounting Standards Update 2014-09 | Minimum Pension Liability Adjustment | Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption									15
Accounting Standards Update 2014-09 | Postretirement Health Coverage | Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of new accounting principle in period of adoption									$ (365)