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Investment Securities Available for Sale (Summary of Available for Sale Investment Securities) (Details) - USD ($) $ in Thousands | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 7,395,265 | $ 6,647,791
Gross Unrealized Gains | 182,653 | 133,385
Gross Unrealized Losses | (11,393) | (2,506)
Fair Value | 7,566,525 | 6,778,670
U.S. Treasury securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 20,254 | 19,855
Gross Unrealized Gains | 0 | 0
Gross Unrealized Losses | 0 | 0
Fair Value | 20,254 | 19,855
U.S. Government agency securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 153,984 | 35,499
Gross Unrealized Gains | 3,056 | 1,042
Gross Unrealized Losses | (426) | 0
Fair Value | 156,614 | 36,541
Mortgage-backed securities issued by U.S. Government agencies |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 1,132,816 | 56,328
Gross Unrealized Gains | 2,655 | 560
Gross Unrealized Losses | (6,079) | (72)
Fair Value | 1,129,392 | 56,816
Mortgage-backed securities issued by U.S. Government sponsored enterprises |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 4,402,051 | 5,079,396
Gross Unrealized Gains | 138,611 | 103,495
Gross Unrealized Losses | (276) | (2,076)
Fair Value | 4,540,386 | 5,180,815
Collateralized mortgage obligations issued by U.S. Government agencies or sponsored enterprises |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 1,331,011 | 629,706
Gross Unrealized Gains | 18,495 | 7,349
Gross Unrealized Losses | (4,222) | (204)
Fair Value | 1,345,284 | 636,851
Commercial mortgage-backed securities issued by U.S. Government agencies or sponsored enterprises |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 334,463 | 357,291
Gross Unrealized Gains | 19,694 | 14,301
Gross Unrealized Losses | 0 | 0
Fair Value | 354,157 | 371,592
State and municipal securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 500 | 2,069
Gross Unrealized Gains | 1 | 6
Gross Unrealized Losses | 0 | 0
Fair Value | 501 | 2,075
Asset-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost |  | 323,237
Gross Unrealized Gains |  | 4,315
Gross Unrealized Losses |  | (152)
Fair Value |  | 327,400
Corporate debt securities and other debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 20,186 | 144,410
Gross Unrealized Gains | 141 | 2,317
Gross Unrealized Losses | (390) | (2)
Fair Value | $ 19,937 | $ 146,725

X
- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563 + Details
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