Impairment of Investment Securities - Schedule of Unrealized Losses and Estimated Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Unrealized Losses On Securities [Line Items]
Estimated Fair Value, Less Than 12 Months	$ 820,209	$ 135,599
Gross Unrealized Losses Less Than 12 Months	(24,588)	(464)
Estimated Fair Value, 12 Months or More	110,947	23,350
Gross Unrealized Losses 12 Months or More	(23,078)	(28,496)
Total Estimated Fair Value	931,156	158,949
Total Gross Unrealized Losses	(47,666)	(28,960)
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Schedule Of Unrealized Losses On Securities [Line Items]
Estimated Fair Value, Less Than 12 Months	2,401	0
Gross Unrealized Losses Less Than 12 Months	(237)	0
Estimated Fair Value, 12 Months or More	21,122	23,316
Gross Unrealized Losses 12 Months or More	(18,280)	(28,496)
Total Estimated Fair Value	23,523	23,316
Total Gross Unrealized Losses	(18,517)	(28,496)
Obligations of U.S. Government [Member] | Mortgage - Backed Securities - Residential [Member]
Schedule Of Unrealized Losses On Securities [Line Items]
Estimated Fair Value, Less Than 12 Months	2,035	0
Gross Unrealized Losses Less Than 12 Months	(59)	0
Estimated Fair Value, 12 Months or More	0	13
Gross Unrealized Losses 12 Months or More	0	0	[1]
Total Estimated Fair Value	2,035	13
Total Gross Unrealized Losses	(59)	0
Obligations of U.S. Government-Sponsored Enterprises [Member] | Mortgage - Backed Securities - Residential [Member]
Schedule Of Unrealized Losses On Securities [Line Items]
Estimated Fair Value, Less Than 12 Months	632,231	76,296
Gross Unrealized Losses Less Than 12 Months	(22,844)	(392)
Estimated Fair Value, 12 Months or More	65,324	21
Gross Unrealized Losses 12 Months or More	(4,319)	0	[1]
Total Estimated Fair Value	697,555	76,317
Total Gross Unrealized Losses	(27,163)	(392)
Obligations of U.S. Government-Sponsored Enterprises [Member] | Other Government - Sponsored Enterprises [Member]
Schedule Of Unrealized Losses On Securities [Line Items]
Estimated Fair Value, Less Than 12 Months	183,542	59,303
Gross Unrealized Losses Less Than 12 Months	(1,448)	(72)
Estimated Fair Value, 12 Months or More	24,501	0
Gross Unrealized Losses 12 Months or More	(479)	0
Total Estimated Fair Value	208,043	59,303
Total Gross Unrealized Losses	$ (1,927)	$ (72)

[1] Gross unrealized losses related to these types of securities are less than $1 thousand.