Indemnifications and Guarantees - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) loan Financial_Institution	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Transaction loan Financial_Institution	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) loan
Guarantor Obligations [Line Items]
Provision for losses at the time of sale	$ 1,843,000	$ 1,254,000	$ 4,005,000	$ 2,034,000
Number of unrelated financial institutions | Financial_Institution	3		3
Derivative transaction held for guarantee | loan	133		133		134
Notional	$ 526,900,000		$ 526,900,000		$ 518,800,000
Aggregate fair value of swaps to customers	10,100,000		10,100,000		$ 10,900,000
Reserves for swap guarantees	$ 0		$ 0
Minimum
Guarantor Obligations [Line Items]
Notional amount maturity period			1 year
Maximum
Guarantor Obligations [Line Items]
Notional amount maturity period			10 years
Secondary Market Loan Sales
Guarantor Obligations [Line Items]
Provision for losses at the time of sale			$ 0
Number of loans repurchased | Transaction			0