Investments (Maturity Information) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Investment securities available for sale
Total investment securities available for sale, cost	$ 5,164,774		$ 5,192,419
Total investment securities available for sale, fair value	5,161,585	[1]	5,226,228	[2]
Investment securities held to maturity
Investment securities held to maturity	1,013	[1]	1,342	[2]
Debt Securities
Investment securities available for sale
Maturing in one year or less, cost	864,992		2,285,159
Maturing in one through five years, cost	2,168,080		1,590,608
Maturing in five through ten years, cost	60		898
Maturing in over ten years, cost	0		0
Maturing in one year or less, fair value	865,925		2,286,403
Maturing in one through five years, fair value	2,168,344		1,592,923
Maturing in five through ten years, fair value	60		880
Maturing in over ten years, fair value	0		0
Equity Securities
Investment securities available for sale
Total investment securities available for sale, cost	543		543
Total investment securities available for sale, fair value	21,224		16,365
Mortgage Backed Securities, Other [Member]
Investment securities available for sale
Total investment securities available for sale, cost	2,131,099		1,315,211
Total investment securities available for sale, fair value	2,106,032		1,329,657
Investment securities held to maturity
Investment securities held to maturity	1,013		1,342
Fair Value	$ 1,080		$ 1,448

[1] Unaudited

[2] Derived from 2012 Annual Report on Form 10-K.