Cash Value of Life Insurance - Summary of Activity in Balance of Cash Value of Life Insurance (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Policies Company Employees	Jun. 30, 2017 USD ($) Policies Company Employees
Increase (Decrease) in Insurance Liabilities [Abstract]
Beginning balance			$ 97,783	$ 95,912
Increase in cash value of life insurance	$ 656	$ 626	1,264	1,311
Gain on death benefit				108
Insurance proceeds receivable reclassified to other assets				(921)
Ending balance	$ 99,047	$ 96,410	99,047	96,410
End of period death benefit			$ 164,649	$ 166,318
Number of policies owned | Policies			182	183
Insurance companies used | Company			13	14
Current and former employees and directors covered | Employees			57	57