Other Comprehensive Income (Loss) - Summary of Reclassification Out of Each Component of Accumulated Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net gain on available for sale securities sold	$ (153)	$ (11)
Tax expense	1,592	1,815
Net income	(3,320)	(3,686)
Amount Reclassified From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net income	(280)
Amount Reclassified From Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Available for Sale [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net gain on available for sale securities sold	(153)	(11)
Tax expense	54	4
Net income	(99)	$ (7)
Amount Reclassified From Accumulated Other Comprehensive Income [Member] | Amortization of Postretirement Benefits Prior Service Costs [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Reduction in salaries and employee benefits	(278)
Tax expense	97
Net income	$ (181)