Cash Value of Life Insurance - Summary of Activity in Balance of Cash Value of Life Insurance (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) company employee policy	Dec. 31, 2019 USD ($) employee company policy	Dec. 31, 2018 USD ($)
Insurance [Line Items]
Beginning balance	$ 117,823	$ 117,318
Increase in cash value of life insurance	2,949	3,029	$ 2,718
Gain on death benefit	498	831	0
Insurance proceeds receivable reclassified to other assets	(2,400)	(3,355)
Ending balance	118,870	117,823	$ 117,318
End of period death benefit	$ 197,379	$ 199,084
Number of policies owned (in policies) | policy	183	189
Insurance companies used (in companies) | company	14	14
Current and former employees and directors covered (in employees) | employee	62	63
FNBB
Insurance [Line Items]
Acquired policies from business combination	$ 0	$ 0