Foreclosed Assets - Summary of Activity in Balance of Foreclosed Assets (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Assets	Dec. 31, 2016 USD ($) Assets	Dec. 31, 2015 USD ($)
Schedule Of Foreclosed Assets Activity [Line Items]
Beginning balance, net	$ 3,986	$ 5,369
Additions/transfers from loans	1,563	2,505
Dispositions/sales	(2,161)	(3,748)
Valuation adjustments	(162)	(140)
Ending balance, net	3,226	3,986	$ 5,369
Ending valuation allowance	$ (200)	$ (314)
Ending number of foreclosed assets | Assets	16	15
Proceeds from sale of foreclosed assets	$ 2,872	$ 4,010
Gain on sale of foreclosed assets	711	262	991
Noncovered [Member]
Schedule Of Foreclosed Assets Activity [Line Items]
Beginning balance, net	3,763	5,369
Additions/transfers from loans	1,563	2,282
Dispositions/sales	(1,938)	(3,748)
Valuation adjustments	(162)	(140)
Ending balance, net	3,226	3,763	$ 5,369
Ending valuation allowance	$ (200)	$ (314)
Ending number of foreclosed assets | Assets	16	14
Proceeds from sale of foreclosed assets	$ 2,656	$ 4,010
Gain on sale of foreclosed assets	718	262
Covered [Member]
Schedule Of Foreclosed Assets Activity [Line Items]
Beginning balance, net	223
Additions/transfers from loans		223
Dispositions/sales	(223)
Ending balance, net		$ 223
Ending number of foreclosed assets | Assets		1
Proceeds from sale of foreclosed assets	216
Gain on sale of foreclosed assets	$ (7)