Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest and dividends on investment securities (taxable)	$ 87	$ 458	$ 576	$ 636
Interest expense	(37,057)	(40,730)	(112,074)	(119,206)
Tax effect	(17,049)	(10,179)	(46,898)	(34,925)
Total net of tax	42,842	35,954	118,056	98,286
Total reclassifications, net of tax	(2,093)	(533)	(5,573)	(1,257)
Unrealized gains on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(6)		162
Non-credit impairment losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	50		336
Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(2,095)		(5,943)
Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Amortization of net loss	(71)	(205)	(215)	(616)
Tax effect	29	86	87	257
Total reclassifications, net of tax	(42)	(119)	(128)	(359)
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(3,578)	(1,323)	(10,146)	(4,651)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized gains on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
(Losses) gains on securities transactions, net	(10)	157	258	2,481
Tax effect	4	(66)	(96)	(1,036)
Total net of tax	(6)	91	162	1,445
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Non-credit impairment losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest and dividends on investment securities (taxable)	87	458	576	636
Tax effect	(37)	(191)	(240)	(265)
Total net of tax	50	267	336	371
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	(3,578)	(1,323)	(10,146)	(4,651)
Tax effect	1,483	551	4,203	1,937
Total net of tax	$ (2,095)	$ (772)	$ (5,943)	$ (2,714)