Changes in Accumulated Other Comprehensive Loss by Component - Rollforward (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 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	(1,834)	(28)
Amounts reclassified from accumulated other comprehensive loss	307	295
Balance at the end of the period	(7,710)	(5,761)
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	(1,834)	(28)
Amounts reclassified from accumulated other comprehensive loss	121
Balance at the end of the period	(2,650)	(28)
Other Postretirement Benefit Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	1,048	807
Amounts reclassified from accumulated other comprehensive loss	(39)	(21)
Balance at the end of the period	1,009	786
Pension Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	(6,294)	(6,835)
Amounts reclassified from accumulated other comprehensive loss	225	316
Balance at the end of the period	$ (6,069)	$ (6,519)