Pension Plan and Employee Benefits - Unobservable Input Reconciliation (Details) - PENSION BENEFITS - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation[Roll Forward]
Fair value of plan assets at beginning of period	$ 444,089	$ 403,715
Fair value of plan assets at end of period	391,933	444,089
SUCCESSOR \| Real estate funds
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation[Roll Forward]
Fair value of plan assets at beginning of period	19,195	18,668
Realized gains (losses)	29	(2,365)
Unrealized gains	391	2,674
Purchases	710	649
Sales	(27)	(431)
Fair value of plan assets at end of period	$ 20,298	$ 19,195

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

+ References

+ Details

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Amount, measured using unobservable input, of decrease in plan asset of defined benefit plan from sale.

+ References

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- Definition

Amount, measured using unobservable input, of increase in plan asset of defined benefit plan from purchase.

+ References

+ Details

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