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Investment Securities and Equity Securities with Readily Determinable Fair Values (Details) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Held-to-maturity securities |  |
Amortized cost | $ 3,400 | $ 3,400
Estimated fair value | 3,400 | 3,400
Carrying Value | 3,400 | 3,400
Available-for-sale securities |  |
Amortized cost | 4,034,746 | 3,054,289
Available for sale debt securities | 4,057,357 | 3,080,768
Total Amortized cost | 4,034,746 | 3,054,289
Total Gross unrealized gains | 31,741 | 35,832
Total Gross unrealized losses | 9,130 | 9,353
Estimate of Fair Value Measurement [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities and equity securities | 4,057,357 | 3,080,768
Reported Value Measurement [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities and equity securities | 4,057,357 | 3,080,768
US Treasury Securities [Member] |  |
Available-for-sale securities |  |
Amortized cost | 945,682 |
US Treasury Securities [Member] | Estimate of Fair Value Measurement [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities | 945,682 |
US Treasury Securities [Member] | Reported Value Measurement [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities | 945,682 |
Collateralized Mortgage Backed Securities [Member] |  |
Available-for-sale securities |  |
Amortized cost | 3,043,953 | 3,006,592
Gross unrealized gains | 28,203 | 32,701
Gross unrealized losses | (9,120) | (9,339)
Collateralized Mortgage Backed Securities [Member] | Estimate of Fair Value Measurement [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities | 3,063,036 | 3,029,954
Collateralized Mortgage Backed Securities [Member] | Reported Value Measurement [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities | 3,063,036 | 3,029,954
US Government Corporations and Agencies Securities [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities | 326,756 | 371,407
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities | 2,736,280 | 2,658,547
US States and Political Subdivisions Debt Securities [Member] |  |
Available-for-sale securities |  |
Amortized cost | 45,111 | 47,697
Gross unrealized gains | 3,538 | 3,131
Gross unrealized losses | (10) | (14)
US States and Political Subdivisions Debt Securities [Member] | Estimate of Fair Value Measurement [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities | 48,639 | 50,814
US States and Political Subdivisions Debt Securities [Member] | Reported Value Measurement [Member] |  |
Available-for-sale securities |  |
Available for sale debt securities | 48,639 | 50,814
Other Debt Obligations [Member] |  |
Held-to-maturity securities |  |
Amortized cost | 3,400 | 3,400
Estimated fair value | 3,400 | 3,400
Carrying Value | $ 3,400 | $ 3,400

X
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