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, 2018	Dec. 31, 2017
Net income	$ 33,449		$ 312,577	$ 238,450
Derivative instruments
Comprehensive income (loss) before tax	0		2,681	647
Income tax benefit (provision)	0		0	0
Derivative instruments, net of tax	0		2,681	647
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax	24,067		20,591	(4,347)
Income tax benefit (provision)	0		0	0
Pension, postretirement and other post-employment benefits, net of tax	24,067		20,591	(4,347)
Available-for-sale securities
Comprehensive income (loss) before tax	387		(343)	(387)
Income tax benefit (provision)	0		0	0
Available-for-sale securities, net of tax	387		(343)	(387)
Total other comprehensive income (loss)	24,454		22,929	(4,087)
Total comprehensive income	$ 57,903		$ 335,506	$ 234,363
Predecessor
Net income		$ 1,242,081
Derivative instruments
Comprehensive income (loss) before tax		(532)
Income tax benefit (provision)		80
Derivative instruments, net of tax		(452)
Pension, postretirement and other post-employment benefits
Comprehensive income (loss) before tax		(1,848)
Income tax benefit (provision)		483
Pension, postretirement and other post-employment benefits, net of tax		(1,365)
Available-for-sale securities
Comprehensive income (loss) before tax		2,968
Income tax benefit (provision)		(1,042)
Available-for-sale securities, net of tax		1,926
Total other comprehensive income (loss)		109
Total comprehensive income		$ 1,242,190