Financial Guarantee Insurance Contracts - Effect of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct Premiums Written	$ (13,480)	$ (22,954)	$ (30,739)	$ (19,304)
Assumed Reinsurance Premiums Written	0	0	0	0
Ceded Reinsurance Premiums Written	22,873	(789)	22,030	(1,832)
Premiums written, net of reinsurance	36,353	22,165	52,769	17,472
Direct Premiums Earned	13,097	27,559	52,596	87,506
Assumed Reinsurance Premiums Earned	19	20	59	59
Ceded Reinsurance Premiums Earned	2,650	1,939	6,598	5,206
Reinsurance on premiums earned, Net	$ 10,466	$ 25,640	$ 46,057	$ 82,359