Indemnifications and Guarantees - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) Transactions Financial_Institution	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Transactions Financial_Institution	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) Transactions
Guarantor Obligations [Line Items]
Provision for losses at the time of sale	$ 1,453,000	$ 333,000	$ 6,012,000	$ 3,013,000
Number of unrelated financial institutions | Financial_Institution	3		3
Derivative transaction held for guarantee | Transactions	114		114		101
Aggregate notional amount	$ 451,500,000		$ 451,500,000		$ 417,900,000
Notional amount maturity period, minimum			2 years
Notional amount maturity period, maximum			10 years 6 months
Aggregate market value of swaps to customers	21,700,000		$ 21,700,000		$ 16,500,000
Loss reserves for swap guarantees	$ 0		0
Secondary Market Loan Sales [Member]
Guarantor Obligations [Line Items]
Provision for losses at the time of sale			$ 0
Number of loans repurchased | Transactions			1