Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance	$ (97,176)	$ (94,476)	$ (98,989)	$ (95,397)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI, net of tax	(1,008)	(648)	(2,821)	(1,569)
Net current-period other comprehensive income (loss)	1,008	648	2,821	1,569
Ending balance	(96,168)	(93,828)	(96,168)	(93,828)
Defined Benefit Pension Items
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance	(96,933)	(94,444)	(98,734)	(95,365)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI, net of tax	(1,002)	(648)	(2,803)	(1,569)
Net current-period other comprehensive income (loss)	1,002	648	2,803	1,569
Ending balance	(95,931)	(93,796)	(95,931)	(93,796)
Actuarial gain (loss) tax amount	317	218	891	528
Other
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance	(243)	(32)	(255)	(32)
Other comprehensive income (loss) before reclassifications	0	0	0	0
Amounts reclassified from AOCI, net of tax	(6)	0	(18)	0
Net current-period other comprehensive income (loss)	6	0	18	0
Ending balance	$ (237)	$ (32)	$ (237)	$ (32)