Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance	$ (94,476)	$ (101,442)	$ (95,397)	$ (102,922)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from AOCI, net of tax	(648)	(2,316)	(1,569)	(3,796)
Net current-period other comprehensive income	648	2,316	1,569	3,796
Ending balance	(93,828)	(99,126)	(93,828)	(99,126)
Defined Benefit Pension Items
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance	(94,444)	(101,475)	(95,365)	(102,955)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from AOCI, net of tax	(648)	(2,316)	(1,569)	(3,796)
Net current-period other comprehensive income	648	2,316	1,569	3,796
Ending balance	(93,796)	(99,159)	(93,796)	(99,159)
Actuarial gain (loss) tax amount	218	777	528	1,274
Other Comprehensive Income (Loss), Other Category
Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance	(32)	33	(32)	33
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from AOCI, net of tax	0	0	0	0
Net current-period other comprehensive income	0	0	0	0
Ending balance	$ (32)	$ 33	$ (32)	$ 33