Capital and Liquidity Requirements - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Percentage of Freddie Mac's liquidity requirement of outstanding principal of TAH loans serviced	8.00%	8.00%
Other Assets [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Outstanding borrower advances	$ 0.1	$ 0.2
Seller/Servicer Agreements [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Amount of capital in excess of aggregate regulatory requirements	$ 321.1