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Amortized Cost and Fair Value of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012
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Comparison of amortized cost and estimated fair value of investment securities, available-for-sale |  |
Total investment securities, weighted yield | 3.06% | 2.71%
Total investment securities, amortized cost | $ 3,300,610 | $ 3,587,677
Total investment securities, gross unrealized gains | 52,064 | 101,778
Total investment securities, gross unrealized losses | (33,721) | (6,450)
Total investment securities, fair value | 3,318,953 | 3,683,005
U.S. government and federal agency |  |
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale |  |
Maturing within one year, weighted yield |  | 1.62%
Maturing within one year, amortized cost |  | 201
Maturing within one year, gross unrealized gains |  | 1
Maturing within one year, gross unrealized losses |  | 0
Maturing within one year, fair value |  | 202
U.S. government sponsored enterprises |  |
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale |  |
Maturing after one year through five years, weighted yield | 2.29% | 2.30%
Maturing after five years through ten years, weighted yield | 1.82% | 2.03%
Total investment securities, weighted yield | 2.29% | 2.29%
Maturing after one year through five years, amortized cost | 11,278 | 17,064
Maturing after five years through ten years, amortized cost | 38 | 44
Total investment securities, amortized cost | 11,316 | 17,108
Maturing after one year through five years, gross unrealized gains | 240 | 371
Maturing after five years through ten years, gross unrealized gains | 0 | 1
Total investment securities, gross unrealized gains | 240 | 372
Maturing after one year through five years, gross unrealized losses | 0 | 0
Maturing after five years through ten years, gross unrealized losses | 0 | 0
Total investment securities, gross unrealized losses | 0 | 0
Maturing after one year through five years, fair value | 11,518 | 17,435
Maturing after five years through ten years, fair value | 38 | 45
Total investment securities, fair value | 11,556 | 17,480
State and local governments |  |
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale |  |
Maturing within one year, weighted yield | 2.18% | 2.01%
Maturing after one year through five years, weighted yield | 2.10% | 2.11%
Maturing after five years through ten years, weighted yield | 3.17% | 2.95%
Maturing after ten years, weighted yield | 4.46% | 4.70%
Total investment securities, weighted yield | 4.10% | 4.29%
Maturing within one year, amortized cost | 6,059 | 4,288
Maturing after one year through five years, amortized cost | 162,569 | 149,497
Maturing after five years through ten years, amortized cost | 57,892 | 38,346
Maturing after ten years, amortized cost | 1,104,890 | 935,897
Total investment securities, amortized cost | 1,331,410 | 1,128,028
Maturing within one year, gross unrealized gains | 52 | 28
Maturing after one year through five years, gross unrealized gains | 3,096 | 4,142
Maturing after five years through ten years, gross unrealized gains | 1,122 | 1,102
Maturing after ten years, gross unrealized gains | 28,571 | 82,823
Total investment securities, gross unrealized gains | 32,841 | 88,095
Maturing within one year, gross unrealized losses | 0 | (2)
Maturing after one year through five years, gross unrealized losses | (431) | (142)
Maturing after five years through ten years, gross unrealized losses | (832) | (99)
Maturing after ten years, gross unrealized losses | (21,604) | (1,362)
Total investment securities, gross unrealized losses | (22,867) | (1,605)
Maturing within one year, fair value | 6,111 | 4,314
Maturing after one year through five years, fair value | 165,234 | 153,497
Maturing after five years through ten years, fair value | 58,182 | 39,349
Maturing after ten years, fair value | 1,111,857 | 1,017,358
Total investment securities, fair value | 1,341,384 | 1,214,518
Corporate bonds |  |
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale |  |
Maturing within one year, weighted yield | 2.10% | 1.73%
Maturing after one year through five years, weighted yield | 2.10% | 2.22%
Maturing after five years through ten years, weighted yield | 2.22% | 2.23%
Total investment securities, weighted yield | 2.10% | 2.19%
Maturing within one year, amortized cost | 73,064 | 18,412
Maturing after one year through five years, amortized cost | 358,034 | 250,027
Maturing after five years through ten years, amortized cost | 11,058 | 16,144
Total investment securities, amortized cost | 442,156 | 284,583
Maturing within one year, gross unrealized gains | 736 | 51
Maturing after one year through five years, gross unrealized gains | 2,890 | 4,018
Maturing after five years through ten years, gross unrealized gains | 0 | 381
Total investment securities, gross unrealized gains | 3,626 | 4,450
Maturing within one year, gross unrealized losses | 0 | 0
Maturing after one year through five years, gross unrealized losses | (2,852) | (238)
Maturing after five years through ten years, gross unrealized losses | (85) | 0
Total investment securities, gross unrealized losses | (2,937) | (238)
Maturing within one year, fair value | 73,800 | 18,463
Maturing after one year through five years, fair value | 358,072 | 253,807
Maturing after five years through ten years, fair value | 10,973 | 16,525
Total investment securities, fair value | 442,845 | 288,795
Collateralized debt obligations |  |
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale |  |
Maturing after ten years, weighted yield |  | 8.03%
Maturing after ten years, amortized cost |  | 1,708
Maturing after ten years, gross unrealized gains |  | 0
Maturing after ten years, gross unrealized losses |  | 0
Maturing after ten years, fair value |  | 1,708
Residential mortgage-backed securities |  |
Comparison of amortized cost and estimated fair value of investment securities, available-for-sale |  |
Total investment securities, weighted yield | 2.44% | 1.95%
Total investment securities, amortized cost | 1,515,728 | 2,156,049
Total investment securities, gross unrealized gains | 15,357 | 8,860
Total investment securities, gross unrealized losses | (7,917) | (4,607)
Total investment securities, fair value | $ 1,523,168 | $ 2,160,302

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