Changes in Accumulated Other Comprehensive Loss by Component - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	$ (6,672)	$ (6,183)
Other comprehensive earning (loss) before reclassifications	(189)	(1,227)
Amounts reclassified from accumulated other comprehensive loss	155	153
Balance at the end of the period	(6,706)	(7,257)
Unrealized Net Loss on Interest Rate Swap
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	(1,195)	(937)
Other comprehensive earning (loss) before reclassifications	(189)	(1,227)
Amounts reclassified from accumulated other comprehensive loss	60	60
Balance at the end of the period	(1,324)	(2,104)
Other Postretirement Benefit Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	937	1,048
Amounts reclassified from accumulated other comprehensive loss	(17)	(20)
Balance at the end of the period	920	1,028
Pension Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	(6,414)	(6,294)
Amounts reclassified from accumulated other comprehensive loss	112	113
Balance at the end of the period	$ (6,302)	$ (6,181)