Retirement and Postretirement Plans - Summary of Components of Net Periodic Benefit Cost for Plans (Details) - USD ($) $ in Thousands	11 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		$ (1,200)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 14,981
Expected return on plan assets	(27,658)
Settlement gain recognized	(1,160)
Net periodic benefit cost (benefit)	(13,837)
OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	22
Interest cost	695
Net periodic benefit cost (benefit)	$ 717