Financial Guarantee Insurance Contracts - Effect of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Written	$ (20,605)	$ (611)	$ (17,259)	$ 3,650
Assumed Reinsurance Premiums Written	0	0	0	0
Ceded Reinsurance Premiums Written	(343)	(224)	(844)	(1,043)
Premiums written, net of reinsurance	20,262	387	16,415	(4,693)
Direct Premiums Earned	10,066	27,339	39,500	59,947
Assumed Reinsurance Premiums Earned	20	19	39	39
Ceded Reinsurance Premiums Earned	2,253	1,522	3,948	3,267
Reinsurance on premiums earned, Net	$ 7,833	$ 25,836	$ 35,591	$ 56,719