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Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands | Jun. 30, 2015 | Dec. 31, 2014
--- | --- | ---
Available-for-sale |  |
Amortized Cost | $ 2,336,693 | $ 2,341,767
Gross Unrealized Gains | 42,135 | 53,468
Gross Unrealized Losses | (16,998) | (7,807)
Fair Value | 2,361,830 | 2,387,428
Held-to-maturity |  |
Amortized Cost | 593,314 | 520,997
Gross Unrealized Gains | 23,308 | 32,925
Gross Unrealized Losses | (7,841) | (2,976)
Fair Value | 608,781 | 550,946
Total |  |
Amortized Cost | 2,930,007 | 2,862,764
Gross Unrealized Gains | 65,443 | 86,393
Gross Unrealized Losses | (24,839) | (10,783)
Fair Value | 2,970,611 | 2,938,374
U.S. government and federal agency |  |
Available-for-sale |  |
Amortized Cost | 51,889 | 44
Gross Unrealized Gains | 13 | 0
Gross Unrealized Losses | (405) | 0
Fair Value | 51,497 | 44
U.S. government sponsored enterprises |  |
Available-for-sale |  |
Amortized Cost | 81,085 | 21,916
Gross Unrealized Gains | 32 | 31
Gross Unrealized Losses | (356) | (2)
Fair Value | 80,761 | 21,945
State and local governments |  |
Available-for-sale |  |
Amortized Cost | 938,088 | 962,365
Gross Unrealized Gains | 29,310 | 40,173
Gross Unrealized Losses | (9,346) | (4,569)
Fair Value | 958,052 | 997,969
Held-to-maturity |  |
Amortized Cost | 593,314 | 520,997
Gross Unrealized Gains | 23,308 | 32,925
Gross Unrealized Losses | (7,841) | (2,976)
Fair Value | 608,781 | 550,946
Corporate bonds |  |
Available-for-sale |  |
Amortized Cost | 355,140 | 313,545
Gross Unrealized Gains | 1,482 | 2,059
Gross Unrealized Losses | (773) | (750)
Fair Value | 355,849 | 314,854
Residential mortgage-backed securities |  |
Available-for-sale |  |
Amortized Cost | 910,491 | 1,043,897
Gross Unrealized Gains | 11,298 | 11,205
Gross Unrealized Losses | (6,118) | (2,486)
Fair Value | $ 915,671 | $ 1,052,616

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- Definition This item represents the cost of available-for-sale and held-to-maturity debt securities, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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