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Investments (Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position) (Details) - USD ($) $ in Thousands | Jun. 30, 2020 | Dec. 31, 2019
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Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | $ 885,412 | $ 611,152
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (9,815) | (7,192)
Available-for-sale securities, estimated fair value, 12 months or longer | 187,916 | 352,025
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (6,981) | (7,287)
Available-for-sale securities, estimated fair value | 1,073,328 | 963,177
Available-for-sale securities, gross unrealized holding losses | (16,796) | (14,479)
Short-term investments, estimated fair value, less than 12 months | 566,873 | 3,316
Short-term investments, gross unrealized holding losses, less than 12 months | (2,772) | (60)
Short-term investments, estimated fair value, 12 months or longer | 0 | 0
Short-term investments, gross unrealized holding losses, 12 months or longer | 0 | 0
Short-term investments, estimated fair value | 566,873 | 3,316
Short-term investments, gross unrealized holding losses | (2,772) | (60)
U.S. Treasury securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 7,675 | 36,862
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (19) | (361)
Available-for-sale securities, estimated fair value, 12 months or longer | 0 | 46,518
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | 0 | (41)
Available-for-sale securities, estimated fair value | 7,675 | 83,380
Available-for-sale securities, gross unrealized holding losses | (19) | (402)
U.S. government-sponsored enterprises [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months |  | 24,148
Available-for-sale securities, gross unrealized holding losses, less than 12 months |  | (197)
Available-for-sale securities, estimated fair value, 12 months or longer |  | 2,868
Available-for-sale securities, gross unrealized holding losses, 12 months or longer |  | (3)
Available-for-sale securities, estimated fair value |  | 27,016
Available-for-sale securities, gross unrealized holding losses |  | (200)
Obligations of states, municipalities and political subdivisions [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 46,271 | 127,836
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (1,009) | (702)
Available-for-sale securities, estimated fair value, 12 months or longer | 3,025 | 6,830
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (23) | (110)
Available-for-sale securities, estimated fair value | 49,296 | 134,666
Available-for-sale securities, gross unrealized holding losses | (1,032) | (812)
Foreign governments [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 173,200 | 162,907
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (4,295) | (3,393)
Available-for-sale securities, estimated fair value, 12 months or longer | 160,104 | 159,888
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (5,648) | (6,005)
Available-for-sale securities, estimated fair value | 333,304 | 322,795
Available-for-sale securities, gross unrealized holding losses | (9,943) | (9,398)
Commercial mortgage-backed securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 2,033 | 202,530
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (14) | (1,126)
Available-for-sale securities, estimated fair value, 12 months or longer | 7,425 | 33,853
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (21) | (256)
Available-for-sale securities, estimated fair value | 9,458 | 236,383
Available-for-sale securities, gross unrealized holding losses | (35) | (1,382)
Residential mortgage-backed securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 3,756 | 11,706
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (35) | (66)
Available-for-sale securities, estimated fair value, 12 months or longer | 0 | 58,162
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | 0 | (451)
Available-for-sale securities, estimated fair value | 3,756 | 69,868
Available-for-sale securities, gross unrealized holding losses | (35) | (517)
Asset-backed securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 359 | 0
Available-for-sale securities, gross unrealized holding losses, less than 12 months | 0 | 0
Available-for-sale securities, estimated fair value, 12 months or longer | 0 | 3,632
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | 0 | (22)
Available-for-sale securities, estimated fair value | 359 | 3,632
Available-for-sale securities, gross unrealized holding losses | 0 | (22)
Corporate bonds [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 85,245 | 41,847
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (1,671) | (1,287)
Available-for-sale securities, estimated fair value, 12 months or longer | 17,362 | 40,274
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (1,289) | (399)
Available-for-sale securities, estimated fair value | 102,607 | 82,121
Available-for-sale securities, gross unrealized holding losses | (2,960) | (1,686)
Total fixed maturities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale securities, estimated fair value, less than 12 months | 318,539 | 607,836
Available-for-sale securities, gross unrealized holding losses, less than 12 months | (7,043) | (7,132)
Available-for-sale securities, estimated fair value, 12 months or longer | 187,916 | 352,025
Available-for-sale securities, gross unrealized holding losses, 12 months or longer | (6,981) | (7,287)
Available-for-sale securities, estimated fair value | 506,455 | 959,861
Available-for-sale securities, gross unrealized holding losses | $ (14,024) | $ (14,419)

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