Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest and dividends on investment securities (taxable)	$ 34	$ 110	$ 178	$ 308
Interest expense	(39,577)	(39,745)	(78,476)	(78,759)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(12,474)	(11,751)	(24,746)	(12,581)
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(1,699)	(1,664)	(3,328)	(3,312)
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	(1,147)	(942)	(724)	(1,834)
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
(Losses) gains on securities transactions, net	(92)	7	2,324	(1)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	37	(3)	(970)	0
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	(55)	4	1,354	(1)
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)	34	110	178	308
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(14)	(46)	(74)	(129)
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	20	64	104	179
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	(1,699)	(1,664)	(3,328)	(3,312)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	708	691	1,386	1,374
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	(991)	(973)	(1,942)	(1,938)
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)	(62)	(410)	(124)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	84	25	170	50
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	$ (121)	$ (37)	$ (240)	$ (74)