Indemnifications and Guarantees - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2016 USD ($) Transactions Financial_Institution	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) Transactions
Guarantor Obligations [Line Items]
Provision for losses at the time of sale	$ 780,000	$ 786,000
Number of unrelated financial institutions | Financial_Institution	5
Derivative transaction held for guarantee | Transactions	123		119
Aggregate notional amount	$ 488,900,000		$ 481,600,000
Notional amount maturity period, minimum	4 years
Notional amount maturity period, maximum	10 years
Aggregate fair value of swaps to customers	$ 27,000,000		$ 18,100,000
Reserves for swap guarantees	0
Secondary Market Loan Sales [Member]
Guarantor Obligations [Line Items]
Provision for losses at the time of sale	$ 0
Number of loans repurchased | Transactions	0