Securities - Summary of amortized cost and fair value by contractual maturity of available for sale securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Due in one year or less, Amortized Cost	$ 1,080	$ 3,583
Due after one year but less than five years, Amortized Cost	47,065	37,747
Due after five years but less than ten years, Amortized Cost	26,615	28,441
Due after ten years, Amortized Cost	9,044	8,002
Amortized Cost	83,804	77,773
Due in one year or less, Fair Value	1,079	3,514
Due after one year but less than five years, Fair Value	46,358	37,425
Due after five years but less than ten years, Fair Value	26,149	28,250
Due after ten years, Fair Value	8,646	7,964
Total available-for-sale securities, Fair Value	$ 82,232	$ 77,153