Commitments and Contingencies - Off-balance Sheet Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Off-balance Sheet Risks, Amount, Liability	$ 385	$ 381
Commitments to Extend Credit [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Off-balance Sheet Risks, Amount, Liability	980,647
Performance Letters Of Credit [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Off-balance Sheet Risks, Amount, Liability	26,570
Standby Letters of Credit [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Off-balance Sheet Risks, Amount, Liability	19,981
Other Letters Of Credit [Member]
Fair Value Off Balance Sheet Risks Disclosure Information [Line Items]
Off-balance Sheet Risks, Amount, Liability	$ 15