Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest and dividends on investment securities (taxable)	$ 489	$ 144
Interest expense	(37,444)	(38,899)
Tax effect	(14,389)	(12,272)
Net Income	36,187	30,341
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(2,971)	(1,629)
Net Income	(1,328)	423
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized Gains and (Losses) on Available for Sale (AFS) Securities
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains on securities transactions, net	271	2,416
Tax effect	(101)	(1,007)
Net Income	170	1,409
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Non-credit Impairment Losses on AFS Securities
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest and dividends on investment securities (taxable)	489	144
Tax effect	(203)	(60)
Net Income	286	84
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized Losses on Derivatives (Cash Flow Hedges) Before Tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(2,971)	(1,629)
Tax effect	1,230	678
Net Income	(1,741)	(951)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Defined Benefit Pension Plans
Reclassification Out Of Accumulated Other Comprehensive Loss
Amortization of net actuarial loss	(72)	(205)
Tax effect	29	86
Net Income	$ (43)	$ (119)