Accumulated Other Comprehensive Income (Schedule of Reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net of tax			$ 0
Pension, Postretirement and Other Postemployment Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net of tax			487
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net of tax			332
Successor
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	$ 549,866		1,150,841
Provision for (benefit from) income taxes	(319)		(1,159)
Net income (loss)	37,160		88,828
Successor | Amortization of prior service credits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI before tax	0		0
Successor | Amortization of actuarial gains (losses), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI before tax	0		0
Successor | Pension settlement
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI before tax	487		487
Successor | Pension, Postretirement and Other Postemployment Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI before tax	487		487
Provision for (benefit from) income taxes	0		0
Net of tax	487		487
Successor | Reclassification out of Accumulated Other Comprehensive Income | Derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues	0		0
Provision for (benefit from) income taxes	0		0
Net income (loss)	0		0
Successor | Reclassification out of Accumulated Other Comprehensive Income | Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Provision for (benefit from) income taxes	0		0
Net income (loss)	0		332
Interest and investment income	$ 0		$ 332
Predecessor
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues		$ 420,298		$ 848,404
Provision for (benefit from) income taxes		245		1,356
Net income (loss)		(175,887)		(382,589)
Predecessor | Amortization of prior service credits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI before tax		2,672		5,344
Predecessor | Amortization of actuarial gains (losses), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI before tax		77		(1,257)
Predecessor | Pension settlement
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI before tax				0
Predecessor | Pension, Postretirement and Other Postemployment Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI before tax		2,749		4,087
Provision for (benefit from) income taxes		0		(481)
Net of tax		2,749		3,606
Predecessor | Reclassification out of Accumulated Other Comprehensive Income | Derivative instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Revenues		96		321
Provision for (benefit from) income taxes		0		(81)
Net income (loss)		96		240
Predecessor | Reclassification out of Accumulated Other Comprehensive Income | Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Provision for (benefit from) income taxes		0		1,038
Net income (loss)		0		(1,857)
Interest and investment income		$ 0		$ (2,895)