Other Comprehensive Income (Loss) - Summary of Reclassifications Out of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	$ (350)		$ 511
Income tax expense	(7,698)		(7,566)
Net of tax	17,029		17,828
Reclassification Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	(148)		504
Reclassification Adjustment [Member] | Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain on securities transactions	(350)		511
Income tax expense	143		(209)
Net of tax	(207)		302
Reclassification Adjustment [Member] | Post-Retirement Obligations [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Compensation and employee benefits	42	[1]	342	[1]
Income tax expense	17		(140)
Net of tax	$ 59		$ 202

[1] This item is included in the computation of net periodic benefit cost. See Note 5. Components of Net Periodic Benefit Cost.