Comprehensive Income/(Loss) - Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income/(Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net securities gains reclassified into earnings	$ 2,251	$ 596	$ 981
Related income tax expense	(823)	(219)	(361)
Net effect on accumulated other comprehensive income/(loss) for the period	5,728	7,054	(9,018)
Amortization of unrealized gain transferred from available-for-sale	357	494	472
Related income tax expense	(132)	(182)	(173)
Net effect on accumulated other comprehensive income/(loss) for the period	225	312	299
Defined benefit pension plan:
Amortization of net loss and prior service costs	(3,046)	(3,205)	(1,516)
Related income tax benefit	1,153	1,201	558
Net effect on accumulated other comprehensive income/(loss) for the period	219	(5,237)	14,810
Amounts Reclassified From Accumulated Other Comprehensive Income/(Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net securities gains reclassified into earnings	(2,251)	(596)	(981)
Related income tax expense	823	219	361
Net effect on accumulated other comprehensive income/(loss) for the period	(1,428)	(377)	(620)
Amortization of unrealized gain transferred from available-for-sale	(357)	(494)	(472)
Related income tax expense	132	182	173
Net effect on accumulated other comprehensive income/(loss) for the period	(225)	(312)	(299)
Defined benefit pension plan:
Amortization of net loss and prior service costs	3,046	3,205	1,516
Related income tax benefit	(1,153)	(1,201)	(558)
Net effect on accumulated other comprehensive income/(loss) for the period	1,893	2,004	958
Total reclassifications for the period	$ 240	$ 1,315	$ 39