Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest and dividends on investment securities (taxable)	$ 0	$ 34	$ 489	$ 178
Interest expense	(37,573)	(39,577)	(75,017)	(78,476)
Tax effect	(15,460)	(12,474)	(29,849)	(24,746)
Net Income	39,027	31,991	75,214	62,332
Total reclassifications, net of tax	(2,152)	(1,147)	(3,480)	(724)
Unrealized gains on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(2)		168
Non-credit impairment losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	0		286
Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(2,107)		(3,848)
Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Amortization of net loss	(72)	(205)	(144)	(410)
Tax effect	29	84	58	170
Total reclassifications, net of tax	(43)	(121)	(86)	(240)
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(3,597)	(1,699)	(6,568)	(3,328)
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	(3)	(92)	268	2,324
Tax effect	1	37	(100)	(970)
Net Income	(2)	(55)	168	1,354
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)	0	34	489	178
Tax effect	0	(14)	(203)	(74)
Net Income	0	20	286	104
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	(3,597)	(1,699)	(6,568)	(3,328)
Tax effect	1,490	708	2,720	1,386
Net Income	$ (2,107)	$ (991)	$ (3,848)	$ (1,942)