Cash Value of Life Insurance - Summary of Activity in Balance of Cash Value of Life Insurance (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Policies Employees Company	Sep. 30, 2016 USD ($) Policies Employees Company
Increase (Decrease) in Insurance Liabilities [Abstract]
Beginning balance			$ 95,912	$ 94,560
Increase in cash value of life insurance	$ 732	$ 709	2,043	2,086
Death benefit receivable in excess of cash value			108	238
Death benefit receivable			(921)	(1,603)
Ending balance	$ 97,142	$ 95,281	97,142	95,281
End of period death benefit			$ 165,006	$ 166,623
Number of policies owned | Policies			183	187
Insurance companies used | Company			14	14
Current and former employees and directors covered | Employees			57	58