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Securities - Summary of Amortized Cost and Fair Values of Securities Available-for-sale (Details) - USD ($) $ in Thousands | Sep. 30, 2020 | Dec. 31, 2019
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Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | $ 1,478,635 | $ 1,183,404
Available-for-sale Securities, Gross Unrealized Gains | 32,937 | 7,593
Available-for-sale Securities, Gross Unrealized Losses | (2,361) | (4,705)
Available-for-sale Securities, Fair Value | 1,509,211 | 1,186,292
U.S. Treasury Notes |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | 25,456 | 41,403
Available-for-sale Securities, Gross Unrealized Gains | 495 | 427
Available-for-sale Securities, Fair Value | 25,951 | 41,830
U.S. Government Agencies |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | 104,253 | 165,162
Available-for-sale Securities, Gross Unrealized Gains | 814 | 542
Available-for-sale Securities, Gross Unrealized Losses | (357) | (754)
Available-for-sale Securities, Fair Value | 104,710 | 164,950
Obligations of States, Municipalities, and Political Subdivisions |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | 103,895 | 92,806
Available-for-sale Securities, Gross Unrealized Gains | 4,417 | 2,075
Available-for-sale Securities, Gross Unrealized Losses |  | (49)
Available-for-sale Securities, Fair Value | 108,312 | 94,832
Agency, Residential Mortgage-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | 807,798 | 490,427
Available-for-sale Securities, Gross Unrealized Gains | 16,594 | 2,163
Available-for-sale Securities, Gross Unrealized Losses | (355) | (2,354)
Available-for-sale Securities, Fair Value | 824,037 | 490,236
Non-Agency, Residential Mortgage-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | 62,775 | 109,501
Available-for-sale Securities, Gross Unrealized Gains | 1,321 | 593
Available-for-sale Securities, Gross Unrealized Losses |  | (272)
Available-for-sale Securities, Fair Value | 64,096 | 109,822
Agency, Commercial Mortgage-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | 256,830 | 159,650
Available-for-sale Securities, Gross Unrealized Gains | 7,415 | 1,092
Available-for-sale Securities, Gross Unrealized Losses | (513) | (1,041)
Available-for-sale Securities, Fair Value | 263,732 | 159,701
Non-Agency, Commercial Mortgage-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | 11,215 | 31,144
Available-for-sale Securities, Gross Unrealized Gains | 428 | 130
Available-for-sale Securities, Fair Value | 11,643 | 31,274
Corporate Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | 56,059 | 48,796
Available-for-sale Securities, Gross Unrealized Gains | 1,364 | 571
Available-for-sale Securities, Gross Unrealized Losses | (215) | (37)
Available-for-sale Securities, Fair Value | 57,208 | 49,330
Asset-Backed Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Available-for-sale Securities, Amortized Cost | 50,354 | 44,515
Available-for-sale Securities, Gross Unrealized Gains | 89 |
Available-for-sale Securities, Gross Unrealized Losses | (921) | (198)
Available-for-sale Securities, Fair Value | $ 49,522 | $ 44,317

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- 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=118939692&loc=d3e27161-111563 + Details
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