Variable Interest Entities - Summary of Carrying Amounts of Assets and Liabilities of Unconsolidated VIEs (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entity, Not Primary Beneficiary [Member] | Servicing Arrangements With Letter Of Credit Reimbursement Obligation [Member]
Variable Interest Entity [Line Items]
Carrying value of assets recorded on consolidated balance sheets	$ 3,918,000	$ 3,924,000
Maximum Exposure to Loss	168,918,000	168,924,000
Size of VIEs	134,616,000	153,070,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Servicing Arrangements With Letter Of Credit Reimbursement Obligation [Member] | Servicing Rights, Net [Member]
Variable Interest Entity [Line Items]
Carrying value of assets recorded on consolidated balance sheets	900,000	1,145,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Servicing Arrangements With Letter Of Credit Reimbursement Obligation [Member] | Servicer And Protective Advances, Net [Member]
Variable Interest Entity [Line Items]
Carrying value of assets recorded on consolidated balance sheets	2,910,000	2,656,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Servicing Arrangements With Letter Of Credit Reimbursement Obligation [Member] | Receivables, Net [Member]
Variable Interest Entity [Line Items]
Carrying value of assets recorded on consolidated balance sheets	108,000	123,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Other Servicing Arrangements [Member]
Variable Interest Entity [Line Items]
Carrying value of assets recorded on consolidated balance sheets	183,000	190,000
Maximum Exposure to Loss	183,000	190,000
Size of VIEs	437,595,000	443,631,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Other Servicing Arrangements [Member] | Servicing Rights, Net [Member]
Variable Interest Entity [Line Items]
Carrying value of assets recorded on consolidated balance sheets	0	0
Variable Interest Entity, Not Primary Beneficiary [Member] | Other Servicing Arrangements [Member] | Servicer And Protective Advances, Net [Member]
Variable Interest Entity [Line Items]
Carrying value of assets recorded on consolidated balance sheets	0	0
Variable Interest Entity, Not Primary Beneficiary [Member] | Other Servicing Arrangements [Member] | Receivables, Net [Member]
Variable Interest Entity [Line Items]
Carrying value of assets recorded on consolidated balance sheets	183,000	$ 190,000
Variable Interest Entities Primary Beneficiary And Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Reimbursement obligation on LOC, if drawn	$ 165,000,000