Accumulated Other Comprehensive Income (Loss) - Summary of Changes in Accumulated Other Comprehensive Loss for Pension Plan Items (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning balance	$ (552)	$ (7,777)	$ (1,325)	$ (7,517)
Other comprehensive income before reclassifications	1,200	196	1,973	(540)
Amounts reclassified from accumulated other comprehensive loss	0	466	0	942
Total other comprehensive income, net of tax	1,200	662	1,973	402
Accumulated other comprehensive loss, beginning balance	648	(7,115)	648	(7,115)
Realized loss on sale	5,438	3,951	10,651	4,224
Income (loss) before equity in loss from unconsolidated affiliates and income taxes	1,591	23,310	(1,196)	533,212
Income tax benefit	(1,862)	(8,690)	(790)	(115,594)
Net (loss) income	(271)	14,609	(1,986)	417,597
Amount Reclassified from Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net (loss) income	0	466	0	942
Defined Benefit Pension Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning balance	0	(5,415)	0	(5,392)
Other comprehensive income before reclassifications	0	(115)	0	(367)
Amounts reclassified from accumulated other comprehensive loss	0	200	0	429
Total other comprehensive income, net of tax	0	85	0	62
Accumulated other comprehensive loss, beginning balance	0	(5,330)	0	(5,330)
Defined Benefit Pension Items | Amount Reclassified from Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Amortization of loss	0	125	0	257
Settlement cost	0	200	0	440
Income (loss) before equity in loss from unconsolidated affiliates and income taxes	0	325	0	697
Income tax benefit	0	(125)	0	(268)
Net (loss) income	0	200	0	429
Unrealized Gains and (Losses) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss, beginning balance	(552)	(2,362)	(1,325)	(2,125)
Other comprehensive income before reclassifications	1,200	311	1,973	(173)
Amounts reclassified from accumulated other comprehensive loss	0	266	0	513
Total other comprehensive income, net of tax	1,200	577	1,973	340
Accumulated other comprehensive loss, beginning balance	648	(1,785)	648	(1,785)
Unrealized Gains and (Losses) on Available-for-Sale Securities | Amount Reclassified from Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Realized loss on sale	0	432	0	833
Income tax benefit	0	(166)	0	(320)
Net (loss) income	$ 0	$ 266	$ 0	$ 513