Investment Securities (Details 2) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Due in One Year or Less	$ 74,862,000	$ 74,862,000
Due After One Year Through Five Years	254,924,000	254,924,000
Due After Five Years Through Ten Years	644,469,000	644,469,000
Due After Ten Years	344,159,000	344,159,000
Available-for-Sale, Total	1,318,414,000	1,318,414,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date [Abstract]
Due in One Year or Less	75,212,000	75,212,000
Due After One Year Through Five Years	259,762,000	259,762,000
Due After Five Years Through Ten Years	635,390,000	635,390,000
Due After Ten Years	347,952,000	347,952,000
Available-for-Sale, Total	1,318,316,000	1,318,316,000
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis [Abstract]
Due in One Year or Less	80,251,000	80,251,000
Due After One Year Through Five Years	334,307,000	334,307,000
Due After Five Years Through Ten Years	99,806,000	99,806,000
Due After Ten Years	348,181,000	348,181,000
Held-to-Maturity, Total	862,545,000	862,545,000
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value [Abstract]
Due in One Year or Less	80,591,000	80,591,000
Due After One Year Through Five Years	336,102,000	336,102,000
Due After Five Years Through Ten Years	100,778,000	100,778,000
Due After Ten Years	346,189,000	346,189,000
Held-to-Maturity, Total	863,660,000	863,660,000
Available-for-Sale:
Amortized Cost	2,269,875,000	2,269,875,000		3,291,685,000
Fair Value	2,277,136,000	2,277,136,000		3,367,557,000
Gross gains and losses from sale of investment securities
Gross realized gains on sale of investment securities			300,000
Gross losses on sale of investment securities	0		300,000
Amortized Cost	4,633,399,000	4,633,399,000		3,595,065,000
Fair Value	4,621,491,000	4,621,491,000		3,687,676,000
Carrying value of investment securities which are pledged	2,600,000,000	2,600,000,000		2,900,000,000
Proceeds from Sale and Maturity of Marketable Securities	0	0
Mortgage-Backed Securities
Available-for-Sale:
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	951,461,000	951,461,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	958,820,000	958,820,000
Amortized Cost	951,461,000	951,461,000		1,600,958,000
Fair Value	958,820,000	958,820,000		1,630,723,000
Held-to-Maturity
HTM, Debt Maturities, w-o single maturity date, amort cost	3,770,854,000	3,770,854,000
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	3,757,831,000	3,757,831,000
Gross gains and losses from sale of investment securities
Amortized Cost	3,770,854,000	3,770,854,000		3,380,897,000
Fair Value	3,757,831,000	3,757,831,000		3,468,306,000
Residential - Government Agencies
Available-for-Sale:
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	702,921,000	702,921,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	717,474,000	717,474,000
Amortized Cost	702,921,000	702,921,000		1,041,669,000
Fair Value	717,474,000	717,474,000		1,068,660,000
Held-to-Maturity
HTM, Debt Maturities, w-o single maturity date, amort cost	3,422,851,000	3,422,851,000
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	3,410,927,000	3,410,927,000
Gross gains and losses from sale of investment securities
Amortized Cost	3,422,851,000	3,422,851,000		3,349,403,000
Fair Value	3,410,927,000	3,410,927,000		3,434,710,000
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	23,829,000	23,829,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	25,263,000	25,263,000
Amortized Cost	23,829,000	23,829,000		35,234,000
Fair Value	25,263,000	25,263,000		37,298,000
Held-to-Maturity
HTM, Debt Maturities, w-o single maturity date, amort cost	23,375,000	23,375,000
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	24,825,000	24,825,000
Gross gains and losses from sale of investment securities
Amortized Cost	23,375,000	23,375,000		31,494,000
Fair Value	24,825,000	24,825,000		33,596,000
Commercial - Government Agencies
Available-for-Sale:
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	224,711,000	224,711,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	216,083,000	216,083,000
Amortized Cost	224,711,000	224,711,000		524,055,000
Fair Value	216,083,000	216,083,000		524,765,000
Held-to-Maturity
HTM, Debt Maturities, w-o single maturity date, amort cost	324,628,000	324,628,000
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	322,079,000	322,079,000
Gross gains and losses from sale of investment securities
Amortized Cost	324,628,000	324,628,000
Fair Value	322,079,000	322,079,000
Maximum [Member]
Gross gains and losses from sale of investment securities
Gross realized gains on sale of investment securities	$ 100,000