Investment Securities (by Maturity buckets and narrative) (Details 2) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis Rolling Maturity[Abstract]
Due in One Year or Less	$ 19,928,000
Due After One Year Through Five Years	287,496,000
Due After Five Years Through Ten Years	653,258,000
Due After Ten Years	108,982,000
Amortized Cost, Total	1,069,664,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Due in One Year or Less	20,091,000
Due After One Year Through Five Years	292,869,000
Due After Five Years Through Ten Years	657,028,000
Due After Ten Years	115,734,000
Fair Value, Total	1,085,722,000
Available-for-sale Securities, Amortized Cost	2,196,994,000	2,245,857,000
Available-for-sale Securities, Fair Value	2,220,913,000	2,243,697,000
Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis, Rolling Maturities (Abstract]
Due in One Year or Less	89,643,000
Due After One Year Through Five Years	408,976,000
Due After Five Years Through Ten Years	198,123,000
Due After Ten Years	222,803,000
Amortized Cost, Total	919,545,000
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Due in One Year or Less	91,049,000
Due After One Year Through Five Years	406,911,000
Due After Five Years Through Ten Years	204,053,000
Due After Ten Years	230,572,000
Fair Value, Total	932,585,000
Held-to-maturity Securities, Amortized Cost	4,557,614,000	4,744,519,000
Held-to-Maturity Securities, Fair Value	4,576,396,000	4,697,587,000
Carrying value of investment securities which are pledged	2,700,000,000	2,600,000,000
Debt Securities Issued by Government Agencies
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	281,038,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	285,892,000
Mortgage-Backed Securities
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	846,292,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	849,299,000
Available-for-sale Securities, Amortized Cost	846,292,000	882,951,000
Available-for-sale Securities, Fair Value	849,299,000	886,115,000
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-maturity Securities, Debt Maturities, Debt Maturities, without Single Maturity Date, Amortized Cost	3,638,069,000
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	3,643,811,000
Held-to-maturity Securities, Amortized Cost	3,638,069,000	3,867,312,000
Held-to-Maturity Securities, Fair Value	3,643,811,000	3,826,026,000
Residential - Government Agencies
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	493,031,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	504,098,000
Available-for-sale Securities, Amortized Cost	493,031,000	641,227,000
Available-for-sale Securities, Fair Value	504,098,000	653,194,000
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-maturity Securities, Debt Maturities, Debt Maturities, without Single Maturity Date, Amortized Cost	3,034,148,000
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	3,045,574,000
Held-to-maturity Securities, Amortized Cost	3,034,148,000	3,523,343,000
Held-to-Maturity Securities, Fair Value	3,045,574,000	3,488,557,000
Residential - U.S. Government Sponsored Enterprises
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	157,672,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	158,993,000
Available-for-sale Securities, Amortized Cost	157,672,000	21,865,000
Available-for-sale Securities, Fair Value	158,993,000	23,268,000
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-maturity Securities, Debt Maturities, Debt Maturities, without Single Maturity Date, Amortized Cost	284,683,000
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	285,742,000
Held-to-maturity Securities, Amortized Cost	284,683,000	21,602,000
Held-to-Maturity Securities, Fair Value	285,742,000	23,025,000
Commercial - Government Agencies
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Rolling Maturities [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis	195,589,000
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value	186,208,000
Available-for-sale Securities, Amortized Cost	195,589,000	219,859,000
Available-for-sale Securities, Fair Value	186,208,000	209,653,000
Held-to-Maturity Securities, Debt Maturities, Single Maturity Date, Fair Value, Rolling Maturities [Abstract]
Held-to-maturity Securities, Debt Maturities, Debt Maturities, without Single Maturity Date, Amortized Cost	319,238,000
Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value	312,495,000
Held-to-maturity Securities, Amortized Cost	319,238,000	322,367,000
Held-to-Maturity Securities, Fair Value	$ 312,495,000	$ 314,444,000