Goodwill and Intangible Assets - Schedule of Estimated Amortization Expense (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
2018	$ 73
2019	130
2020	114
2021	110
2022	110
Thereafter	710
Net Carrying Amount	1,247	$ 1,279
MSRs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
2018	21
2019	42
2020	42
2021	42
2022	42
Thereafter	581
Net Carrying Amount	770	743
Core deposit intangibles [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
2018	52
2019	88
2020	72
2021	68
2022	68
Thereafter	129
Net Carrying Amount	$ 477	$ 536