Cash Value of Life Insurance - Summary of Activity in Balance of Cash Value of Life Insurance (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) Policies Employees Company	Mar. 31, 2017 USD ($) Policies Employees Company
Increase (Decrease) in Insurance Liabilities [Abstract]
Beginning balance	$ 97,783	$ 95,912
Increase in cash value of life insurance	608	685
Gain on death benefit		107
Insurance proceeds receivable reclassified to other assets		(921)
Ending balance	98,391	95,783
End of period death benefit	$ 159,640	$ 164,574
Number of policies owned | Policies	182	183
Insurance companies used | Company	14	14
Current and former employees and directors covered | Employees	57	58