Business Combination - Schedule of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Jan. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill created	$ 20,221	$ 20,221		$ 208
OLCB [Member]
Business Acquisition [Line Items]
Cash			$ 46,159
Loans			259,373
Available for sale securities			9,996
FHLB stock, at cost			1,256
Premises and equipment			2,940
Accrued interest			679
Other intangible assets			2,426
Other real estate owned			89
Other assets			7,240
Total assets acquired			330,158
Deposits assumed			266,279
Federal Home Loan Bank advances			23,500
Repurchase agreements and other borrowings			10,771
Accrued expenses and other liabilities			2,581
Total liabilities assumed			303,131
Goodwill created			$ 19,168