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Bank segment - Components of investment securities (Details) $ in Thousands | Mar. 31, 2021 USD ($) issue | Dec. 31, 2020 USD ($) issue
--- | --- | ---
Debt Securities, Available-for-sale [Abstract] |  |
Amortized cost | $ 2,340,488 |
Estimated fair value | 2,305,257 |
Debt Securities, Held-to-maturity [Abstract] |  |
Amortized cost | 295,046 | $ 226,947
Held-to-maturity investment securities | 285,599 | 229,963
American Savings Bank (ASB) |  |
Debt Securities, Available-for-sale [Abstract] |  |
Amortized cost | 2,340,488 | 1,943,114
Gross unrealized gains | 18,173 | 30,454
Gross unrealized losses | (53,404) | (3,151)
Estimated fair value | $ 2,305,257 | $ 1,970,417
Gross unrealized losses, Less than 12 months, Number of issues | issue | 93 | 22
Gross unrealized losses, Less than 12 months, Fair value | $ 1,617,916 | $ 373,924
Gross unrealized losses, Less than 12 months, Amount | $ (53,385) | $ (3,151)
Gross unrealized losses, 12 months or longer, Number of issues | issue | 1 | 0
Gross unrealized losses, 12 months or longer, Fair value | $ 958 | $ 0
Gross unrealized losses, 12 months or more, amount | (19) | 0
Debt Securities, Held-to-maturity [Abstract] |  |
Amortized cost | 295,046 | 226,947
Gross unrealized gains | 2,812 | 3,846
Gross unrealized losses | (12,259) | (830)
Held-to-maturity investment securities | $ 285,599 | $ 229,963
Less than 12 months: Number of issues | issue | 16 | 7
Less than 12 Months: Fair value | $ 220,908 | $ 114,152
Less than 12 Months: Amount | $ (12,259) | $ (830)
12 months or longer: Number of issues | issue | 0 | 0
12 months or longer: Fair value | $ 0 | $ 0
12 months or longer: Amount | 0 | 0
U.S. Treasury and federal agency obligations | American Savings Bank (ASB) |  |
Debt Securities, Available-for-sale [Abstract] |  |
Amortized cost | 55,969 | 60,260
Gross unrealized gains | 1,719 | 2,062
Gross unrealized losses | (41) | 0
Estimated fair value | $ 57,647 | $ 62,322
Gross unrealized losses, Less than 12 months, Number of issues | issue | 1 | 0
Gross unrealized losses, Less than 12 months, Fair value | $ 4,908 | $ 0
Gross unrealized losses, Less than 12 months, Amount | $ (41) | $ 0
Gross unrealized losses, 12 months or longer, Number of issues | issue | 0 | 0
Gross unrealized losses, 12 months or longer, Fair value | $ 0 | $ 0
Gross unrealized losses, 12 months or more, amount | 0 | 0
Mortgage-backed securities* | American Savings Bank (ASB) |  |
Debt Securities, Available-for-sale [Abstract] |  |
Amortized cost | 2,239,311 | 1,825,893
Gross unrealized gains | 15,404 | 26,817
Gross unrealized losses | (53,363) | (3,151)
Estimated fair value | $ 2,201,352 | $ 1,849,559
Gross unrealized losses, Less than 12 months, Number of issues | issue | 92 | 22
Gross unrealized losses, Less than 12 months, Fair value | $ 1,613,008 | $ 373,924
Gross unrealized losses, Less than 12 months, Amount | $ (53,344) | $ (3,151)
Gross unrealized losses, 12 months or longer, Number of issues | issue | 1 | 0
Gross unrealized losses, 12 months or longer, Fair value | $ 958 | $ 0
Gross unrealized losses, 12 months or more, amount | (19) | 0
Debt Securities, Held-to-maturity [Abstract] |  |
Amortized cost | 295,046 | 226,947
Gross unrealized gains | 2,812 | 3,846
Gross unrealized losses | (12,259) | (830)
Held-to-maturity investment securities | $ 285,599 | $ 229,963
Less than 12 months: Number of issues | issue | 16 | 7
Less than 12 Months: Fair value | $ 220,908 | $ 114,152
Less than 12 Months: Amount | $ (12,259) | $ (830)
12 months or longer: Number of issues | issue | 0 | 0
12 months or longer: Fair value | $ 0 | $ 0
12 months or longer: Amount | 0 | 0
Corporate bonds | American Savings Bank (ASB) |  |
Debt Securities, Available-for-sale [Abstract] |  |
Amortized cost | 29,781 | 29,776
Gross unrealized gains | 1,050 | 1,575
Gross unrealized losses | 0 | 0
Estimated fair value | $ 30,831 | $ 31,351
Gross unrealized losses, Less than 12 months, Number of issues | issue | 0 | 0
Gross unrealized losses, Less than 12 months, Fair value | $ 0 | $ 0
Gross unrealized losses, Less than 12 months, Amount | $ 0 | $ 0
Gross unrealized losses, 12 months or longer, Number of issues | issue | 0 | 0
Gross unrealized losses, 12 months or longer, Fair value | $ 0 | $ 0
Gross unrealized losses, 12 months or more, amount | 0 | 0
Mortgage revenue bonds | American Savings Bank (ASB) |  |
Debt Securities, Available-for-sale [Abstract] |  |
Amortized cost | 15,427 | 27,185
Gross unrealized gains | 0 | 0
Gross unrealized losses | 0 | 0
Estimated fair value | $ 15,427 | $ 27,185
Gross unrealized losses, Less than 12 months, Number of issues | issue | 0 | 0
Gross unrealized losses, Less than 12 months, Fair value | $ 0 | $ 0
Gross unrealized losses, Less than 12 months, Amount | $ 0 | $ 0
Gross unrealized losses, 12 months or longer, Number of issues | issue | 0 | 0
Gross unrealized losses, 12 months or longer, Fair value | $ 0 | $ 0
Gross unrealized losses, 12 months or more, amount | $ 0 | $ 0

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