Impairment of Investment Securities - Schedule of Unrealized Losses and Estimated Fair Values (Detail) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	$ 252,333,000		$ 820,209,000
Grous Unrealized Losses Less Than 12 Months	(681,000)	(24,588,000)
Estimated Fair Value, 12 Months or More	537,557,000		110,947,000
Gross Unrealized Losses 12 Months or More	(27,740,000)	(23,078,000)
Total Estimated Fair Value	789,890,000		931,156,000
Total Gross Unrealized Losses	(28,421,000)	(47,666,000)
US Government Agencies Residential Mortgage-backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months			2,035,000
Grous Unrealized Losses Less Than 12 Months		(59,000)
Estimated Fair Value, 12 Months or More			0
Gross Unrealized Losses 12 Months or More		0
Total Estimated Fair Value			2,035,000
Total Gross Unrealized Losses		(59,000)
Obligations of U.S. Government-Sponsored Enterprises - Mortgage-Backed Securities - Residential [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	117,662,000		632,231,000
Grous Unrealized Losses Less Than 12 Months	(373,000)	(22,844,000)
Estimated Fair Value, 12 Months or More	432,719,000		65,324,000
Gross Unrealized Losses 12 Months or More	(13,434,000)	(4,319,000)
Total Estimated Fair Value	550,381,000		697,555,000
Total Gross Unrealized Losses	(13,807,000)	(27,163,000)
Obligations of U.S. Government-Sponsored Enterprises - Other Government-Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	131,555,000		183,542,000
Grous Unrealized Losses Less Than 12 Months	(238,000)	(1,448,000)
Estimated Fair Value, 12 Months or More	80,916,000		24,501,000
Gross Unrealized Losses 12 Months or More	(565,000)	(479,000)
Total Estimated Fair Value	212,471,000		208,043,000
Total Gross Unrealized Losses	(803,000)	(1,927,000)
Obligations of States and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	490,000
Grous Unrealized Losses Less Than 12 Months	(5,000)
Estimated Fair Value, 12 Months or More	0
Gross Unrealized Losses 12 Months or More	0
Total Estimated Fair Value	490,000
Total Gross Unrealized Losses	(5,000)
Pooled Trust Preferred Collateralized Debt Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Estimated Fair Value, Less Than 12 Months	2,626,000		2,401,000
Grous Unrealized Losses Less Than 12 Months	(65,000)	(237,000)
Estimated Fair Value, 12 Months or More	23,922,000		21,122,000
Gross Unrealized Losses 12 Months or More	(13,741,000)	(18,280,000)
Total Estimated Fair Value	26,548,000		23,523,000
Total Gross Unrealized Losses	(13,806,000)	(18,517,000)
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total Estimated Fair Value	$ 0	$ 0