Changes in Accumulated Other Comprehensive Loss by Component - Rollforward (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 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	(4,837)	(4,799)
Amounts reclassified from accumulated other comprehensive loss	1,514	309
Impact due to adoption	(557)
Balance at the end of the period	(6,137)	(10,539)
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	(4,837)	(4,799)
Amounts reclassified from accumulated other comprehensive loss	1,685	152
Balance at the end of the period	(8,175)	(6,177)
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	(171)	(173)
Balance at the end of the period	$ 2,038	1,945
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		330
Balance at the end of the period		$ (6,307)