Servicing of Residential Loans - Schedule of Fair Value Assumptions, Fair Value of Servicing Rights on Date of Sale (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Transfers and Servicing [Abstract]
Weighted-average life in years	6 years 2 months	6 years 6 months	7 years 1 month
Weighted-average discount rate	12.47%	11.90%	9.43%
Weighted-average conditional prepayment rates	9.15%	8.19%	7.67%
Weighted-average conditional default rate	0.34%	0.39%	0.73%