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Investment Securities (Details) (USD $) In Thousands, unless otherwise specified | Dec. 31, 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 | 5,372,594 | 5,423,189
Gross unrealized gains | 65,104 | 119,670
Gross unrealized losses | (133,119) | (17,844)
Total investment securities | 5,304,579 | 5,525,015
Estimated fair value |  |
Available-for-sale securities |  |
Total investment securities | 5,304,579 | 5,525,015
Carrying value |  |
Available-for-sale securities |  |
Total investment securities | 5,304,579 | 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 | 5,096,165 | 5,186,652
Gross unrealized gains | 56,110 | 94,585
Gross unrealized losses | (124,574) | (16,033)
Residential mortgage-backed securities | Estimated fair value |  |
Available-for-sale securities |  |
Total investment securities | 5,027,701 | 5,265,204
Residential mortgage-backed securities | Carrying value |  |
Available-for-sale securities |  |
Total investment securities | 5,027,701 | 5,265,204
Mortgage-backed securities by Ginnie Mae |  |
Available-for-sale securities |  |
Total investment securities | 1,799,807 | 2,035,742
Mortgage-backed securities by Fannie Mae and Freddie Mac |  |
Available-for-sale securities |  |
Total investment securities | 3,200,042 | 3,196,602
Mortgage-backed securities by non-government entities |  |
Available-for-sale securities |  |
Total investment securities | 27,852 | 32,860
Obligations of states and political subdivisions |  |
Available-for-sale securities |  |
Amortized cost | 248,354 | 216,962
Gross unrealized gains | 8,063 | 23,504
Gross unrealized losses | (8,007) | (1,791)
Obligations of states and political subdivisions | Estimated fair value |  |
Available-for-sale securities |  |
Total investment securities | 248,410 | 238,675
Obligations of states and political subdivisions | Carrying value |  |
Available-for-sale securities |  |
Total investment securities | 248,410 | 238,675
Equity Securities |  |
Available-for-sale securities |  |
Amortized cost | 28,075 | 19,575
Gross unrealized gains | 931 | 1,581
Gross unrealized losses | (538) | (20)
Equity Securities | Estimated fair value |  |
Available-for-sale securities |  |
Total investment securities | 28,468 | 21,136
Equity Securities | Carrying value |  |
Available-for-sale securities |  |
Total investment securities | $ 28,468 | $ 21,136

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