Accumulated Other Comprehensive Loss - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017		Sep. 30, 2016
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes		$ 5,005	$ 4,445	$ (19,630)		$ 4,646
Income tax provision		2,389	1,104	7,505		1,486
Net income (loss)		2,616	3,341	(27,135)		3,160
Reclassification out of Accumulated Other Comprehensive Income
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	[1]	(142)	(56)	(142)		(292)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of prior-service cost
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior-service cost	[2],[3]	(227)	(89)	(227)		(266)
Income (loss) before income taxes		(227)	(89)	(227)	[2]	(266)	[2]
Income tax provision		85	33	85		100
Net income (loss)		(142)	$ (56)	$ (142)	[2]	(166)	[2]
Reclassification out of Accumulated Other Comprehensive Income | Recognition of gain on sale of investment
Schedule of Reclassifciations Out of Accumulated Other Comprehensive Income [Line Items]
Recognition of gain on sale of investment		0				(200)	[1]
Income (loss) before income taxes		0				(200)	[1]
Income tax provision		0				74
Net income (loss)		$ 0				$ (126)	[1]

[1] Amounts in parentheses indicate credits to profit/loss

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

[3] This accumulated other comprehensive loss component is included in the computation of net periodic benefit cost (see Note 6).