Changes in Accumulated Other Comprehensive Income (Loss) by Component - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at the beginning of the period	$ (1,053)	$ (5,495)
Other comprehensive gain (loss) before reclassifications	3,517	(213)
Amounts reclassified from accumulated other comprehensive income (loss)	721	719
Balance at the end of the period	3,185	(4,989)
Unrealized Net Gain (Loss) on Interest Rate Swap
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at the beginning of the period	(3,524)	(7,608)
Other comprehensive gain (loss) before reclassifications	3,517	(213)
Amounts reclassified from accumulated other comprehensive income (loss)	762	777
Balance at the end of the period	755	(7,044)
Other Postretirement Benefit Liability
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at the beginning of the period	2,471	2,113
Amounts reclassified from accumulated other comprehensive income (loss)	(41)	(58)
Balance at the end of the period	$ 2,430	$ 2,055