Comprehensive Income - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (7,913)	$ (1,778)
Net Unrealized Gains on Available For Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, before tax	(8,870)	2,145
Accumulated other comprehensive loss, tax effect	3,729	(902)
Accumulated other comprehensive loss	(5,141)	1,243
Unfunded Status of Supplemental Retirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, before tax	(4,714)	(5,735)
Accumulated other comprehensive loss, tax effect	1,982	2,411
Accumulated other comprehensive loss	(2,732)	(3,324)
Joint Beneficiary Agreement Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, before tax	(40)	303
Accumulated other comprehensive loss	$ (40)	$ 303