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Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Held-to-maturity securities
Amortized cost	$ 2,400	$ 2,400
Estimated fair value	2,400	2,400
Carrying value	2,400	2,400
Available-for-sale securities
Amortized cost	5,470,103	5,423,189
Gross unrealized gains	81,235	119,670
Gross unrealized losses	(102,588)	(17,844)
Total investment securities	5,448,750	5,525,015
Estimated fair value
Available-for-sale securities
Total investment securities	5,448,750	5,525,015
Carrying value
Available-for-sale securities
Total investment securities	5,448,750	5,525,015
Other securities
Held-to-maturity securities
Amortized cost	2,400	2,400
Estimated fair value	2,400	2,400
Carrying value	2,400	2,400
Residential mortgage-backed securities
Available-for-sale securities
Amortized cost	5,197,331	5,186,652
Gross unrealized gains	70,436	94,585
Gross unrealized losses	(95,581)	(16,033)
Residential mortgage-backed securities | Estimated fair value
Available-for-sale securities
Total investment securities	5,172,186	5,265,204
Residential mortgage-backed securities | Carrying value
Available-for-sale securities
Total investment securities	5,172,186	5,265,204
Mortgage-backed securities by Ginnie Mae
Available-for-sale securities
Total investment securities	1,894,858	2,035,742
Mortgage-backed securities by Fannie Mae and Freddie Mac
Available-for-sale securities
Total investment securities	3,248,329	3,196,602
Mortgage-backed securities by non-government entities
Available-for-sale securities
Total investment securities	28,999	32,860
Obligations of states and political subdivisions
Available-for-sale securities
Amortized cost	244,697	216,962
Gross unrealized gains	9,758	23,504
Gross unrealized losses	(6,724)	(1,791)
Obligations of states and political subdivisions | Estimated fair value
Available-for-sale securities
Total investment securities	247,731	238,675
Obligations of states and political subdivisions | Carrying value
Available-for-sale securities
Total investment securities	247,731	238,675
Equity Securities
Available-for-sale securities
Amortized cost	28,075	19,575
Gross unrealized gains	1,041	1,581
Gross unrealized losses	(283)	(20)
Equity Securities | Estimated fair value
Available-for-sale securities
Total investment securities	28,833	21,136
Equity Securities | Carrying value
Available-for-sale securities
Total investment securities	$ 28,833	$ 21,136

X

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Amount of accumulated unrealized gain before deducting unrealized loss on investments in available-for-sale securities impacting investments.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

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