Capital Requirements and Restrictions on Retained Earnings - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 Event CapitalCategory	Dec. 31, 2017 USD ($)
Securities Financing Transaction [Line Items]
Number of capital categories provided by PCA regulation | CapitalCategory	5
Number of events resulting in change in Bank's capital category | Event	0
2015 [Member]
Securities Financing Transaction [Line Items]
Capital conservation buffer phase ratio	0.00%
2019 [Member]
Securities Financing Transaction [Line Items]
Capital conservation buffer phase ratio	2.50%
2016 [Member]
Securities Financing Transaction [Line Items]
Capital conservation buffer phase ratio	0.625%
Scenario, Forecast [Member]
Securities Financing Transaction [Line Items]
Accumulated net earnings | $		$ 25,073