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Investments (Details) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2021 USD ($) security | Jun. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) security | Jun. 30, 2020 USD ($) | Dec. 31, 2020 USD ($) security
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | $ 6,682,052 |  | $ 6,682,052 |  | $ 6,317,164
Fair Value | 6,964,409 |  | 6,964,409 |  | 6,661,596
Assets held by insurance regulatory requirements | 13,900 |  | 13,900 |  | 14,100
Assets held in trust for the benefit of contractual counterparties | 185,600 |  | $ 185,600 |  | 160,300
Collateral, market value to principal balance of FHLB (as a percent) |  |  | 102.00% |  |
FHLB advance, collateral pledged | $ 163,300 |  | $ 163,300 |  | $ 163,900
Number of securities in unrealized loss position (in securities) | security | 336 |  | 336 |  | 109
Total fixed income securities |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | $ 6,682,052 |  | $ 6,682,052 |  | $ 6,317,164
Allowance for Expected Credit Loss | 0 | $ 0 | 0 | $ 0 | (49)
Gross Unrealized Gains | 294,061 |  | 294,061 |  | 349,140
Gross Unrealized Losses | (11,704) |  | (11,704) |  | (4,659)
Fair Value | 6,964,409 |  | 6,964,409 |  | 6,661,596
Proceeds from sales of fixed income securities |  |  | 140,100 | 448,500 |
Gross realized gains, fixed income securities | 2,300 | 7,300 | 5,300 | 12,400 |
Gross realized losses, fixed income securities | 400 | 3,700 | 700 | 5,000 |
Impairment charges recognized on securities with the intent to sell | 0 | $ 0 | 0 | $ 300 |
Increase (decrease) in credit allowance for the period |  |  | (49) |  |
U.S. Treasury securities and obligations of U.S. government corporations and agencies |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | 235,822 |  | 235,822 |  | 264,531
Allowance for Expected Credit Loss | 0 |  | 0 |  | 0
Gross Unrealized Gains | 647 |  | 647 |  | 1,164
Gross Unrealized Losses | (149) |  | (149) |  | (2)
Fair Value | 236,320 |  | 236,320 |  | 265,693
Obligations of U.S. states and political subdivisions |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | 2,339,194 |  | 2,339,194 |  | 2,083,568
Allowance for Expected Credit Loss | 0 |  | 0 |  | 0
Gross Unrealized Gains | 161,787 |  | 161,787 |  | 166,557
Gross Unrealized Losses | (2,087) |  | (2,087) |  | (256)
Fair Value | 2,498,894 |  | 2,498,894 |  | 2,249,869
Corporate debt securities |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | 2,847,402 |  | 2,847,402 |  | 2,690,860
Allowance for Expected Credit Loss | 0 |  | 0 |  | 0
Gross Unrealized Gains | 114,625 |  | 114,625 |  | 155,156
Gross Unrealized Losses | (5,966) |  | (5,966) |  | (1,728)
Fair Value | 2,956,061 |  | 2,956,061 |  | 2,844,288
ABS |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | 154,031 |  | 154,031 |  | 203,807
Allowance for Expected Credit Loss | 0 |  | 0 |  | (49)
Gross Unrealized Gains | 1,803 |  | 1,803 |  | 2,946
Gross Unrealized Losses | (101) |  | (101) |  | (18)
Fair Value | 155,733 |  | 155,733 |  | 206,686
RMBS |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | 377,315 |  | 377,315 |  | 425,532
Allowance for Expected Credit Loss | 0 |  | 0 |  | 0
Gross Unrealized Gains | 4,284 |  | 4,284 |  | 6,472
Gross Unrealized Losses | (2,396) |  | (2,396) |  | (838)
Fair Value | 379,203 |  | 379,203 |  | 431,166
CMBS |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | 318,470 |  | 318,470 |  | 312,572
Allowance for Expected Credit Loss | 0 |  | 0 |  | 0
Gross Unrealized Gains | 9,899 |  | 9,899 |  | 16,055
Gross Unrealized Losses | (934) |  | (934) |  | (1,125)
Fair Value | 327,435 |  | 327,435 |  | 327,502
CLOs |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | 396,070 |  | 396,070 |  | 310,616
Allowance for Expected Credit Loss | 0 |  | 0 |  | 0
Gross Unrealized Gains | 952 |  | 952 |  | 566
Gross Unrealized Losses | (65) |  | (65) |  | (692)
Fair Value | 396,957 |  | 396,957 |  | 310,490
Foreign government debt |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost | 13,748 |  | 13,748 |  | 4,485
Allowance for Expected Credit Loss | 0 |  | 0 |  | 0
Gross Unrealized Gains | 64 |  | 64 |  | 224
Gross Unrealized Losses | (6) |  | (6) |  | 0
Fair Value | $ 13,806 |  | $ 13,806 |  | 4,709
Commercial paper |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Amortized Cost |  |  |  |  | 21,193
Allowance for Expected Credit Loss |  |  |  |  | 0
Gross Unrealized Gains |  |  |  |  | 0
Gross Unrealized Losses |  |  |  |  | 0
Fair Value |  |  |  |  | $ 21,193

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