Financial Guarantee Insurance Contracts - Additional Information (Detail) £ in Thousands		3 Months Ended								12 Months Ended
	Jun. 11, 2014	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 GBP (£)	Dec. 31, 2015 GBP (£)	Dec. 31, 2014 GBP (£)	Dec. 31, 2013 USD ($)
Insurance [Line Items]
Amount Of Insured Par Outstanding Ceded To Reinsurer		$ 6,086,000,000								$ 6,086,000,000
Ceded Principal Outstanding Major Reinsurer Percentage										7.00%
Deferred Ceded Premiums And Reinsurance Recoverables		100,042,000								$ 100,042,000
Accrued rate of interest on outstanding policy obligations (percent)	5.10%									5.10%		5.10%
Weighted average period of future premiums										9 years	9 years 2 months 12 days
Losses and loss expense reserves ceded to reinsurers		30,767,000				$ 44,059,000				$ 30,767,000	$ 44,059,000
Subrogation recoveries, net of reinsurance		(1,878,740,000)				(2,800,149,000)				(1,878,740,000)	(2,800,149,000)
Letters of Credit Outstanding, Amount		122,912,000								122,912,000
Financial Guarantee Outstanding Principal Ceded To Third Parties		7,027,000,000								7,027,000,000
Successor [Member]
Insurance [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered		(349,000)				(60,000)				(349,000)	(60,000)	$ (517,000)
Financial Guarantee Insurance Contracts, Premium Receivable		661,337,000				831,575,000				661,337,000	831,575,000	1,000,607,000				$ 1,453,021,000
Financial Guarantee Gross Outstanding Principal Assumed From Third Parties		243,700,000				245,900,000				243,700,000	245,900,000
Reinsurance Payable		42,529,000				53,494,000				$ 42,529,000	$ 53,494,000
Transactions with non-investment grade internal ratings										25.00%	27.00%
Non-investment grade RMBS on total premiums receivable										8.00%	8.00%
Percentage of student loan transactions on total premium receivables										3.00%	5.00%
Percentage related to asset-backed transaction										4.00%	5.00%
Uncollectable premium receivables		9,186,000				15,240,000				$ 9,186,000	$ 15,240,000
Past due premiums on policies insuring non-investment grade obligations amount		500								500
Accelerated premium revenue for retired obligations										52,416,000	137,400,000	29,964,000
Reinsurance recoveries of losses included in losses and loss expenses										5,421,000	47,085,000	21,164,000
Losses and loss expense reserves ceded to reinsurers		30,767,000				44,059,000				30,767,000	44,059,000	100,355,000				$ 122,357,000
Intangible amortization expense		40,152,000	$ 44,553,000	$ 39,013,000	$ 50,890,000	54,357,000	$ 39,680,000	$ 38,088,000	$ 37,432,000	174,608,000	169,557,000	151,830,000
Insurance intangible asset		962,080,000				1,212,112,000				962,080,000	1,212,112,000
Accumulated amortization on insurance intangible asset		572,339,000				414,454,000				572,339,000	414,454,000
Successor [Member] | Insurance Intangible Asset [Member]
Insurance [Line Items]
Intangible amortization expense										$ 174,608,000	$ 169,557,000	151,830,000
Loss Reserves [Member] | Successor [Member]
Insurance [Line Items]
Weighted average risk-free rate used to discount loss reserves										2.70%	2.40%
United Kingdom, Pounds
Insurance [Line Items]
Financial Guarantee Insurance Contracts, Premium Receivable		$ 177,878,000				$ 226,994,000				$ 177,878,000	$ 226,994,000	$ 275,374,000	£ 144,393	£ 154,135	£ 176,703