Deposits - Interest Expense on Deposits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest Expense Deposits [Abstract]
Interest bearing demand deposits and money market accounts	$ 1,874	$ 1,012	$ 1,006
Savings accounts	112	124	161
Certificates of deposit	6,451	4,786	5,359
Total	$ 8,437	$ 5,922	$ 6,526