Investments (Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Investment securities available for sale:
Fair Value, Less than 12 months	$ 645,300	$ 1,173,274
Unrealized Losses, Less than 12 months	1,698	2,203
Fair Value, 12 months or more	317,685	832,420
Unrealized Losses, Greater than 12 months	4,024	10,043
Fair Value, Total	962,985	2,005,694
Unrealized Losses, Total	5,722	12,246
U. S. Treasury
Investment securities available for sale:
Fair Value, Less than 12 months	13,024	338,612
Unrealized Losses, Less than 12 months	2	151
Fair Value, 12 months or more	0	1,015
Unrealized Losses, Greater than 12 months	0	1
Fair Value, Total	13,024	339,627
Unrealized Losses, Total	2	152
Government Agency
Investment securities available for sale:
Fair Value, Less than 12 months	69,660	261,288
Unrealized Losses, Less than 12 months	51	247
Fair Value, 12 months or more	0	0
Unrealized Losses, Greater than 12 months	0	0
Fair Value, Total	69,660	261,288
Unrealized Losses, Total	51	247
Mortgage Backed Securities, Other [Member]
Investment securities available for sale:
Fair Value, Less than 12 months	562,616	573,374
Unrealized Losses, Less than 12 months	1,645	1,805
Fair Value, 12 months or more	317,685	831,405
Unrealized Losses, Greater than 12 months	4,024	10,042
Fair Value, Total	880,301	1,404,779
Unrealized Losses, Total	5,669	11,847
State, County and Municipal
Investment securities available for sale:
Unrealized Losses, Total		$ 0

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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