Investment Securities - Proceeds from Sale, Gross Gains (Losses) Realized on Sales, Maturities and Other-Than-Temporary Impairment Charges Related to Securities Available for Sale (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Proceeds from Sale of Available-for-sale Securities	$ 0	$ 0
Sales Transactions:
Gross gains	0	0
Gross losses	0	0
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments	0	0
Maturities and impairment
Gross Gains	652	0
Gross Losses	0	0
Other Than Temporary Impairment	0	0
Gain Losses Maturities And Impairment	652	0
Net gains and impairment	$ 652	$ 0