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Incentive and Deferred Compensation Plans (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Oct. 01, 2016	Dec. 31, 2018	Dec. 31, 2017	Jan. 31, 2016
Annual Incentive Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Accrued bonuses						$ 6.6
Payments to employees	$ 8.7
Annual Incentive Plan \| Minimum
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Incentive plans, payout percentages of target values						0.00%
Annual Incentive Plan \| Maximum
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Incentive plans, payout percentages of target values						200.00%
Performance Incentive Plan \| Minimum
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Incentive plans, payout percentages of target values								0.00%
Performance Incentive Plan \| Maximum
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Incentive plans, payout percentages of target values								200.00%
Successor
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation plan assets to be distributed to participants							$ 5.1
Successor \| Other Postretirement Benefits Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Retirement plan, employer matching contribution, percent of match			100.00%			100.00%	100.00%
Retirement plan, employer matching contribution, percent of employees' gross pay (up to)			10.00%			10.00%	10.00%
Retirement plan, employer matching contribution, vesting period			4 years			4 years	4 years
Retirement plan, cost recognized			$ 0.9			$ 2.8	$ 3.6
Percent of employee contributions vesting immediately			100.00%			100.00%	100.00%
Successor \| Performance Incentive Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Payments to employees		$ 15.8	$ 7.1
Predecessor \| Other Postretirement Benefits Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Retirement plan, employer matching contribution, percent of match					100.00%
Retirement plan, employer matching contribution, percent of employees' gross pay (up to)					10.00%
Retirement plan, employer matching contribution, vesting period					4 years
Retirement plan, cost recognized					$ 4.9
Percent of employee contributions vesting immediately					100.00%
Predecessor \| Performance Incentive Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Payments to employees				$ 17.8