Changes in Accumulated Other Comprehensive Loss by Component - Rollforward (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	$ (2,814)	$ (6,049)
Other comprehensive gain (loss) before reclassifications	(4,612)	(3,596)
Amounts reclassified from accumulated other comprehensive loss	800	175
Impact due to adoption	(557)
Balance at the end of the period	(6,626)	(9,470)
Unrealized Net Loss on Interest Rate Swap
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	(5,023)	(1,530)
Other comprehensive gain (loss) before reclassifications	(4,612)	(3,596)
Amounts reclassified from accumulated other comprehensive loss	914	70
Balance at the end of the period	(8,721)	(5,056)
Other Postretirement Benefit Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period	2,209	2,118
Amounts reclassified from accumulated other comprehensive loss	(114)	(115)
Balance at the end of the period	$ 2,095	2,003
Pension Liability
Changes to accumulated other comprehensive loss by component
Balance at the beginning of the period		(6,637)
Amounts reclassified from accumulated other comprehensive loss		220
Balance at the end of the period		$ (6,417)