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Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Available-for-sale |  |
Amortized Cost | $ 2,580,520 | $ 1,771,504
Gross Unrealized Gains | 23,360 | 22,433
Gross Unrealized Losses | (32,217) | (15,694)
Total | 2,571,663 | 1,778,243
Held-to-maturity |  |
Amortized Cost | 297,915 | 648,313
Gross Unrealized Gains | 1,380 | 20,346
Gross Unrealized Losses | (11,039) | (8,573)
Fair Value | 288,256 | 660,086
Debt Securities, Available-for-sale and Held-to-maturity [Abstract] |  |
Amortized Cost | 2,878,435 | 2,419,817
Gross Unrealized Gains | 24,740 | 42,779
Gross Unrealized Losses | (43,256) | (24,267)
Fair Value | 2,859,919 | 2,438,329
U.S. government and federal agency |  |
Available-for-sale |  |
Amortized Cost | 23,757 | 31,216
Gross Unrealized Gains | 54 | 54
Gross Unrealized Losses | (162) | (143)
Total | 23,649 | 31,127
U.S. government sponsored enterprises |  |
Available-for-sale |  |
Amortized Cost | 120,670 | 19,195
Gross Unrealized Gains | 52 | 0
Gross Unrealized Losses | (514) | (104)
Total | 120,208 | 19,091
State and local governments |  |
Available-for-sale |  |
Amortized Cost | 844,636 | 614,366
Gross Unrealized Gains | 18,936 | 20,299
Gross Unrealized Losses | (11,322) | (5,164)
Total | 852,250 | 629,501
Held-to-maturity |  |
Amortized Cost | 297,915 | 648,313
Gross Unrealized Gains | 1,380 | 20,346
Gross Unrealized Losses | (11,039) | (8,573)
Fair Value | 288,256 | 660,086
Corporate bonds |  |
Available-for-sale |  |
Amortized Cost | 292,052 | 216,443
Gross Unrealized Gains | 378 | 802
Gross Unrealized Losses | (1,613) | (483)
Total | 290,817 | 216,762
Residential mortgage backed securities |  |
Available-for-sale |  |
Amortized Cost | 808,537 | 785,960
Gross Unrealized Gains | 628 | 1,253
Gross Unrealized Losses | (16,250) | (7,930)
Total | 792,915 | 779,283
Commercial mortgage backed securities |  |
Available-for-sale |  |
Amortized Cost | 490,868 | 104,324
Gross Unrealized Gains | 3,312 | 25
Gross Unrealized Losses | (2,356) | (1,870)
Total | $ 491,824 | $ 102,479

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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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- Definition Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 + Details
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