Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest and dividends on investment securities (taxable)	$ 458	$ 198	$ 636	$ 506
Interest expense	(40,730)	(40,791)	(119,206)	(119,550)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(10,179)	(10,654)	(34,925)	(23,235)
Net Income	35,954	27,682	98,286	91,037
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(1,323)	(1,674)	(4,651)	(4,986)
Net Income	(533)	(834)	(1,257)	(2,668)
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	157	103	2,481	102
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(66)	(43)	(1,036)	(43)
Net Income	91	60	1,445	59
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)	458	198	636	506
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(191)	(83)	(265)	(212)
Net Income	267	115	371	294
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	(1,323)	(1,674)	(4,651)	(4,986)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	551	701	1,937	2,075
Net Income	(772)	(973)	(2,714)	(2,911)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Defined Benefit Pension Plans
Reclassification Out Of Accumulated Other Comprehensive Loss
Amortization of net actuarial loss	(205)	(63)	(616)	(187)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	86	27	257	77
Net Income	$ (119)	$ (36)	$ (359)	$ (110)