Investments Equity Investments (Details) - Successor [Member] - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Other investments	$ 411,604		$ 431,630
Real Estate [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	33,030		33,154
Hedge Funds, Multi-strategy [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	0		53,054
Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	179,856		136,603
Illiquid Investments [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	66,922		67,787
Insurance Linked [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	32,360		22,666
Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	60,605		53,675
Equity investments in pooled funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 372,773		366,939
Readily determinable fair value [Member] \| Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments		$ 2,914	$ 2,823