Accumulated Other Comprehensive Loss (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	$ (102,922,000)	$ (93,347,000)
Other comprehensive income (loss) before reclassifications, net of tax	(5,416,000)	6,525,000
Amounts reclassified from accumulated other comprehensive loss, net of tax	12,941,000	3,270,000
Net current-period other comprehensive income (loss)	7,525,000	9,795,000
Reclassification of disproportionate tax effects from AOCI		19,370,000
Accumulated other comprehensive loss, ending balance	(95,397,000)	(102,922,000)	$ (93,347,000)
Other comprehensive income (loss) before reclassifications, tax amount	(22,000)	(136,000)	102,000
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	(102,955,000)	(93,676,000)
Other comprehensive income (loss) before reclassifications, net of tax	(5,351,000)	6,880,000
Amounts reclassified from accumulated other comprehensive loss, net of tax	12,941,000	3,270,000
Net current-period other comprehensive income (loss)	7,590,000	10,150,000
Reclassification of disproportionate tax effects from AOCI		19,429,000
Accumulated other comprehensive loss, ending balance	(95,365,000)	(102,955,000)	(93,676,000)
Other comprehensive income (loss) before reclassifications, tax amount	(1,803,000)	2,814,000
Amounts reclassified from AOCI, tax amount	4,360,000	1,338,000
Other
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated other comprehensive loss, beginning balance	33,000	329,000
Other comprehensive income (loss) before reclassifications, net of tax	(65,000)	(355,000)
Amounts reclassified from accumulated other comprehensive loss, net of tax	0	0
Net current-period other comprehensive income (loss)	(65,000)	(355,000)
Reclassification of disproportionate tax effects from AOCI		(59,000)
Accumulated other comprehensive loss, ending balance	(32,000)	33,000	$ 329,000
Other comprehensive income (loss) before reclassifications, tax amount	(22,000)	(136,000)
Amounts reclassified from AOCI, tax amount	$ 0	$ 0