Investment Securities (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Amortized cost and fair values of investment securities available for sale by contractual maturity
Securities available for sale, debt securities due in one year or less, amortized cost	$ 45,629
Securities available for sale, debt securities due after one year through five years, amortized cost	231,892
Securities available for sale, debt securities due after five years through ten years, amortized cost	534,809
Securities available for sale, debt securities due after ten years, amortized cost	69,513
Total available for sale debt securities, amortized cost	881,843
Securities available for sale, debt securities due in one year or less, fair value	46,380
Securities available for sale, debt securities due after one year through five years, fair value	240,348
Securities available for sale, debt securities due after five years through ten years, fair value	571,046
Securities available for sale, debt securities due after ten years, fair value	73,133
Total available for sale debt securities, Fair value	930,907
Investment securities available for sale, amortized cost	4,335,354	4,775,400
Investment securities available for sale, at fair value	4,496,198	4,937,483
Amortized cost and fair values of investment securities held to maturity
Securities held to maturity, debt securities due in one year or less, amortized cost	0
Securities held to maturity, debt securities due after one year through five years, amortized cost	0
Securities held to maturity, debt securities due after five years through ten years, amortized cost	5,785
Securities held to maturity, debt securities due after ten years, amortized cost	16,067
Total held to maturity debt securities, amortized Cost	21,852
Securities held to maturity, debt securities due in one year or less, fair value	0
Securities held to maturity, debt securities due in one year through five years, fair value	0
Securities held to maturity, debt securities due after five years through ten years, fair value	5,771
Securities held to maturity, debt securities due after ten years, fair value	15,952
Total held to maturity, debt securities, fair value	21,723
Residential mortgage-related securities [Member]
Amortized cost and fair values of investment securities available for sale by contractual maturity
Investment securities available for sale, amortized cost	3,381,526	3,674,696
Investment securities available for sale, at fair value	3,490,520	3,785,590
Commercial Mortgage Backed Securities [Member]
Amortized cost and fair values of investment securities available for sale by contractual maturity
Investment securities available for sale, amortized cost	71,965	16,647
Investment securities available for sale, at fair value	74,725	18,543
Asset-backed Securities [Member]
Amortized cost and fair values of investment securities available for sale by contractual maturity
Investment securities available for sale, amortized cost		188,439
Investment securities available for sale, at fair value		187,732
Equity Securities [Member]
Amortized cost and fair values of investment securities available for sale by contractual maturity
Investment securities available for sale, amortized cost	20
Investment securities available for sale, at fair value	$ 46