Cash Value of Life Insurance - Summary of Activity in Balance of Cash Value of Life Insurance (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Policies Company Employees	Dec. 31, 2017 USD ($) Policies Company Employees	Dec. 31, 2016 USD ($)	Jul. 06, 2018 USD ($)
Insurance [Line Items]
Beginning balance	$ 97,783	$ 95,912
Increase in cash value of life insurance	2,718	2,685	$ 2,717
Gain on death benefit		108
Insurance proceeds receivable reclassified to other assets		(922)
Ending balance	117,318	97,783	$ 95,912
End of period death benefit	$ 200,249	$ 165,587
Number of policies owned | Policies	196	182
Insurance companies used | Company	14	14
Current and former employees and directors covered | Employees	66	57
FNBB [Member]
Insurance [Line Items]
Acquired policies from business combination	$ 16,817			$ 16,817