Loan Sales and Variable Interest Entities - Summary of Credit Risk Transfer Agreements (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Carrying value of CRT Agreements:
Restricted cash included in Other assets	$ 180,992
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member] | Credit Risk Transfer Agreements [Member]
During the period:
UPB of mortgage loans transferred and sold under CRT Agreements	1,923,113
Deposits of restricted cash	66,706
Gains (losses) recognized on CRT agreements included in Net gain on investments
Realized	2,536
Resulting from valuation changes	(6,679)
Gains (losses) recognized on net derivative related to credit risk transactions	(4,143)
Payments made to settle losses	0
UPB of mortgage loans subject to credit guarantee obligation	5,931,409	$ 4,546,265
Delinquency (in UPB)
Current-89 days delinquent	5,930,936	4,546,265
90 or more days delinquent	473	0
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member] | Derivative Assets [Member] | Credit Risk Transfer Agreements [Member]
Carrying value of CRT Agreements:
Net derivative asset included in Derivative assets	0	593
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member] | Other Assets [Member] | Credit Risk Transfer Agreements [Member]
Carrying value of CRT Agreements:
Restricted cash included in Other assets	213,536	147,000
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure [Member] | Derivative Liabilities [Member] | Credit Risk Transfer Agreements [Member]
Carrying value of CRT Agreements:
Net derivative liability included in Derivative liabilities	$ 4,218	$ 0