Investment Securities (Amortized Cost and Estimated Fair Value of Investment Securities Held-To-Maturity and Securities Available-For-Sale) (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Available-For-Sale Securities [Member]	Dec. 31, 2011 Available-For-Sale Securities [Member]	Sep. 30, 2012 Collateralized Mortgage Obligation ("CMO") [Member] Available-For-Sale Securities [Member]	Dec. 31, 2011 Collateralized Mortgage Obligation ("CMO") [Member] Available-For-Sale Securities [Member]		Dec. 30, 2011 Collateralized Mortgage Obligation ("CMO") [Member] Trading Securities [Member]	Sep. 30, 2011 Collateralized Mortgage Obligation ("CMO") [Member] Trading Securities [Member]	Dec. 31, 2011 Federal National Mortgage Association ("FNMA") [Member] Available-For-Sale Securities [Member]	Dec. 31, 2011 Federal Home Loan Mortgage Corporation ("FHLMC") [Member] Available-For-Sale Securities [Member]	Dec. 31, 2011 Government National Mortgage Association ("GNMA") [Member] Available-For-Sale Securities [Member]	Sep. 30, 2012 Collateralized Mortgage Backed Securities [Member]	Sep. 30, 2012 Collateralized Mortgage Backed Securities [Member] Federal National Mortgage Association ("FNMA") [Member] Available-For-Sale Securities [Member]	Sep. 30, 2012 Collateralized Mortgage Backed Securities [Member] Federal Home Loan Mortgage Corporation ("FHLMC") [Member] Available-For-Sale Securities [Member]	Sep. 30, 2012 Collateralized Mortgage Backed Securities [Member] Government National Mortgage Association ("GNMA") [Member] Available-For-Sale Securities [Member]	Sep. 30, 2012 Reverse Mortgages [Member] Available-For-Sale Securities [Member]	Dec. 31, 2011 Reverse Mortgages [Member] Available-For-Sale Securities [Member]	Sep. 30, 2012 U.S. Government And Government Sponsored Enterprises ("GSE") [Member] Available-For-Sale Securities [Member]	Dec. 31, 2011 U.S. Government And Government Sponsored Enterprises ("GSE") [Member] Available-For-Sale Securities [Member]	Sep. 30, 2012 States And Political Subdivisions [Member] Available-For-Sale Securities [Member]	Dec. 31, 2011 States And Political Subdivisions [Member] Available-For-Sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 881,469,000	$ 840,584,000	$ 881,469,000	$ 840,584,000	$ 247,991,000	$ 323,980,000	[1]	$ 12,432,000	$ 12,590,000	$ 320,019,000	$ 93,305,000	$ 60,991,000	$ 828,200,000	$ 446,296,000	$ 70,110,000	$ 63,757,000	$ (552,000)	$ (646,000)	$ 50,747,000	$ 38,776,000	$ 3,120,000	$ 4,159,000
Gross Unrealized Gains			28,775,000	21,427,000	7,462,000	6,933,000	[1]			9,379,000	1,781,000	3,033,000		15,193,000	2,246,000	3,537,000			308,000	262,000	29,000	39,000
Gross Unrealized Losses	189,000		(189,000)	(2,649,000)	(131,000)	(2,527,000)	[1]			(44,000)		(57,000)		(54,000)					(3,000)	(13,000)	(1,000)	(8,000)
Fair Value	$ 910,055,000	$ 859,362,000	$ 910,055,000	$ 859,362,000	$ 255,322,000	$ 328,386,000	[1]	$ 12,432,000	$ 12,590,000	$ 329,354,000	$ 95,086,000	$ 63,967,000		$ 461,435,000	$ 72,356,000	$ 67,294,000	$ (552,000)	$ (646,000)	$ 51,052,000	$ 39,025,000	$ 3,148,000	$ 4,190,000

[1] Includes agency CMO and SASCO 2002 RM-1 Class O securities classified as available-for-sale