Financial Guarantee Liability - Summary of Provisions for Risk Sharing (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Guarantees [Abstract]
Increase (decrease) to financial guarantee liability	$ (17)	$ (22)	$ (359)
Decrease (increase) to credit enhancement asset	0	10	147
Increase (decrease) to contingent liability	0	0	6
Total expense	$ (17)	$ (12)	$ (206)