Financial Guarantee Insurance Contracts Financial Guarantee Insurance Contracts - Components of Loss and Loss Expense Reserves and Subrogation Recoverable (Details) - Successor [Member] - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ (568)	$ (1,404)	$ (349)
Loss Reserves Ceded To Reinsurers	47,034	30,108	30,767	$ 44,059
Policyholder Benefits and Claims Incurred, Ceded	16,469	(7,607)
Liability for Unpaid Claims and Claims Adjustment Expense, Net	3,876,244	$ 3,620,673	3,665,271	$ 2,814,754
Loss and loss expense reserves	4,582,153		4,380,769
Subrogation recoverable	(658,875)		(684,731)
Claim liability reported on Balance Sheet, before reinsurance	3,923,278		3,696,038
Unpaid Claims-Claims [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	2,418,005		2,411,105
Subrogation recoverable	581,533		583,042
Claim liability reported on Balance Sheet, before reinsurance	2,999,538		2,994,147
Unpaid Claims-Accrued Interest [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	600,510		529,703
Subrogation recoverable	148,878		132,139
Claim liability reported on Balance Sheet, before reinsurance	749,388		661,842
Present Value of Expected Net Cash Flows- Claims and Loss Expenses [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	2,869,074		2,681,198
Subrogation recoverable	41,217		68,419
Claim liability reported on Balance Sheet, before reinsurance	2,910,291		2,749,617
Present Value of Expected Net Cash Flows-Recoveries [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	(1,158,779)		(1,098,096)
Subrogation recoverable	(1,430,503)		(1,468,331)
Claim liability reported on Balance Sheet, before reinsurance	(2,589,282)		(2,566,427)
Unearned Premium Reserve [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Loss and loss expense reserves	(146,657)		(143,141)
Subrogation recoverable	0		0
Claim liability reported on Balance Sheet, before reinsurance	$ (146,657)		$ (143,141)