Business Combination - Schedule of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Jan. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill created	$ 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