Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net loss	$ (2,913,142)	$ (558,353)	$ (641,832)
Derivative instruments
Comprehensive income (loss) before tax	(3,477)	3,102	(2,626)
Income tax benefit (provision)	1,252	(1,117)	947
Derivatives Qualifying as Hedges, Adjustment, Net of Tax	(2,225)	1,985	(1,679)
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax	(5,592)	(44,143)	77,201
Income tax benefit (provision)	2,011	15,891	(27,803)
Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(3,581)	(28,252)	49,398
Available-for-sale securities
Comprehensive income (loss) before tax	1,185	(12,788)	10,190
Income tax benefit (provision)	(435)	4,604	(3,710)
Available-for-sale Securities Adjustment, Net of Tax	750	(8,184)	6,480
Total other comprehensive income (loss)	(5,056)	(34,451)	54,199
Total comprehensive loss	$ (2,918,198)	$ (592,804)	$ (587,633)

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income. Excludes changes in equity resulting from investments by owners and distributions to owners.

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