Recent Developments Including Mergers and Acquisitions - Additional Information (Detail) $ in Thousands			12 Months Ended
	Jan. 12, 2018	Jul. 31, 2017 shares	Dec. 31, 2017 USD ($) Community	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Oct. 08, 2015 USD ($)
Business Combination Separately Recognized Transactions [Line Items]
Goodwill			$ 54,042	$ 54,042	$ 54,042
Number of additional banking communities | Community			2
COMMON STOCK [Member]
Business Combination Separately Recognized Transactions [Line Items]
Stock split description			On July 31, 2017, the Company completed a two-for-one stock split of the Company’s outstanding shares of common stock.
Stock split conversion ratio		2
Stock payable in form of dividend, payable date		Jul. 31, 2017
Stock payable in form of dividend, record date		Jul. 17, 2017
Additional shares received by stockholders for each share held | shares		1
Bank of Commerce [Member]
Business Combination Separately Recognized Transactions [Line Items]
Total assets acquired						$ 196,000
Loans						147,000
Deposits						175,000
Equity capital						$ 22,000
Percentage of voting interests acquired						100.00%
Intangibles assets, net						$ 7,100
Goodwill						$ 9,400
Subsequent Event [Member] | First Bank & Trust Company [Member]
Business Combination Separately Recognized Transactions [Line Items]
Date of acquisition	Jan. 12, 2018
Subsequent Event [Member] | First Bank of Chandler [Member]
Business Combination Separately Recognized Transactions [Line Items]
Date of acquisition	Jan. 12, 2018