Goodwill and Intangible Assets - Schedule of Estimated Amortization Expense (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
2017	$ 134
2018	151
2019	128
2020	112
2021	108
Thereafter	727
Net Carrying Amount	1,360	$ 1,784
MSRs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
2017	30
2018	40
2019	40
2020	40
2021	40
Thereafter	530
Net Carrying Amount	720	662
Core deposit intangibles [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
2017	104
2018	111
2019	88
2020	72
2021	68
Thereafter	197
Net Carrying Amount	$ 640	$ 1,122