Basis of Presentation and Significant Accounting Policies FX gain (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Foreign Currency Transaction Gain (Loss), before Tax		$ 21,116	$ (39,128)	$ (17,010)
Successor [Member]
Foreign Currency Transaction Gain (Loss), before Tax	$ (4,769)	30,179	5,816
Lossandlossreserves [Member]
Foreign Currency Transaction Gain (Loss), before Tax		28,939	(77,578)	(24,838)
Gain (Loss) on Investments [Member]
Foreign Currency Transaction Gain (Loss), before Tax		(4,769)	30,179	5,816
Premiums Receivable [Member]
Foreign Currency Transaction Gain (Loss), before Tax	$ (1,904)	8,003	(2,555)
Unrealized Gains Or Losses On Credit Derivative Contracts [Member]
Foreign Currency Transaction Gain (Loss), before Tax		$ (1,150)	$ 32	$ 3,981