Mortgage-Backed Securities - Year Originated (Detail) - Non-Agency RMBS	Jun. 30, 2020	Dec. 31, 2019
Origination Year as a Percentage of Outstanding Principal Balance:
2003 (and prior)	1.90%	1.30%
2004	1.60%	1.50%
2005	11.20%	10.70%
2006	52.00%	52.90%
2007	26.90%	26.60%
2008 and later	6.40%	7.00%
Total	100.00%	100.00%