Transfers of Residential Loans - Summary of Cash Flows Related to Transfers of Residential Loans Accounted for as Sales (Detail) (Residential Loan Transfers Accounted for as Sales [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Residential Loan Transfers Accounted for as Sales [Member]
Residential Loan Transfers [Line Items]
Proceeds received from transfers, net of fees	$ 19,118,420	$ 15,293,601	$ 15,985
Servicing fees collected	63,420	11,212	0
Repurchases of previously transferred loans	$ 8,186	$ 0	$ 0