Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Oct. 01, 2016	Dec. 31, 2017	Dec. 31, 2015
Net income (loss)	$ 33,449		$ 238,450
Derivative instruments
Comprehensive income (loss) before tax	0		647
Income tax benefit (provision)	0		0
Derivatives Qualifying as Hedges, Adjustment, Net of Tax	0		647
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax	24,067		(4,347)
Income tax benefit (provision)	0		0
Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	24,067		(4,347)
Available-for-sale securities
Comprehensive income (loss) before tax	387		(387)
Income tax benefit (provision)	0		0
Available-for-sale Securities Adjustment, Net of Tax	387		(387)
Total other comprehensive income (loss)	24,454		(4,087)
Total comprehensive income (loss)	$ 57,903		$ 234,363
Predecessor
Net income (loss)		$ 1,242,081		$ (2,913,142)
Derivative instruments
Comprehensive income (loss) before tax		(532)		(3,477)
Income tax benefit (provision)		80		1,252
Derivatives Qualifying as Hedges, Adjustment, Net of Tax		(452)		(2,225)
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax		(1,848)		(5,592)
Income tax benefit (provision)		483		2,011
Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax		(1,365)		(3,581)
Available-for-sale securities
Comprehensive income (loss) before tax		2,968		1,185
Income tax benefit (provision)		(1,042)		(435)
Available-for-sale Securities Adjustment, Net of Tax		1,926		750
Total other comprehensive income (loss)		109		(5,056)
Total comprehensive income (loss)		$ 1,242,190		$ (2,918,198)