Changes in Accumulated Other Comprehensive Loss by Component - Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	$ (6,183)	$ (6,028)
Other comprehensive earning (loss) before reclassifications	(1,101)	(764)
Amounts reclassified from accumulated other comprehensive loss	612	609
Balance at the end of the period	(6,672)	(6,183)
Unrealized Net Loss on Interest Rate Swap
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	(937)
Other comprehensive earning (loss) before reclassifications	(500)	(937)
Amounts reclassified from accumulated other comprehensive loss	242
Balance at the end of the period	(1,195)	(937)
Other Postretirement Benefit Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	1,048	807
Other comprehensive earning (loss) before reclassifications	(32)	285
Amounts reclassified from accumulated other comprehensive loss	(79)	(44)
Balance at the end of the period	937	1,048
Pension Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	(6,294)	(6,835)
Other comprehensive earning (loss) before reclassifications	(569)	(112)
Amounts reclassified from accumulated other comprehensive loss	449	653
Balance at the end of the period	$ (6,414)	$ (6,294)