Comprehensive Income - Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net effect on accumulated other comprehensive income for the period			$ (3,085)	$ (4,819)
Defined benefit pension plan (2):
Total reclassifications for the period			(1,274)	33
Amounts Reclassified From Accumulated Other Comprehensive Income/(Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net securities gains reclassified into earnings	$ (11)	$ (583)	(32)	(831)
Related income tax expense	4	214	12	306
Net effect on accumulated other comprehensive income for the period	(7)	(369)	(20)	(525)
Amortization of unrealized gain transferred from available-for-sale	(104)	(84)	(317)	(354)
Related income tax expense	38	31	118	130
Net effect on accumulated other comprehensive income for the period	(66)	(53)	(199)	(224)
Defined benefit pension plan (2):
Amortization of net loss and prior service costs	808	382	2,397	1,134
Related income tax benefit	(296)	(140)	(904)	(418)
Net effect on accumulated other comprehensive income for the period	512	242	1,493	716
Total reclassifications for the period	$ 439	$ (180)	$ 1,274	$ (33)