CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Income (Loss)	$ (945,731)	$ 568,032	$ 204,554
Cash flow hedges:
Total cash flow hedges	0	(12,178)	(32,018)
Pension and postretirement plans:
Amortization of net benefit obligation at transition, net of tax of $0, $8 and $112, respectively	0	14	207
Amortization of prior service cost, net of tax of $0, $87 and $90, respectively	0	161	167
Amortization of net loss, net of tax of $10,676, $7,676 and $4,472, respectively	19,828	14,256	8,306
Current period change in fair value of pension and postretirement plans, net of tax of $1,779, ($2,722), and $6,237, respectively	3,305	(5,056)	11,582
Total pension and postretirement plans	23,133	9,375	20,262
Comprehensive Income (Loss)	(922,598)	565,229	192,798
Commodity contracts
Cash flow hedges:
Current period change in fair value value of derivative instruments, net of tax	0	37	(10,866)
Reclassification adjustment for derivative instruments, net of tax	0	(13,399)	(22,124)
Interest rate swap
Cash flow hedges:
Current period change in fair value value of derivative instruments, net of tax	0	(298)	(148)
Reclassification adjustment for derivative instruments, net of tax	$ 0	$ 1,482	$ 1,120