Capital and Liquidity Requirements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
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%
Other Assets [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Outstanding borrower advances	$ 0.1	$ 0.1
Seller/Servicer Agreements [Member]
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Amount of capital in excess of aggregate regulatory requirements	$ 426.0