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Investment Information - Securities lending agreements (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
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Disclosure Investment Information [Abstract] |  |
Fair value of cash collateral received on securities lending | $ 0 | $ 0
Fair value of non-cash collateral received on securities lending | 0 | 301,100
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable | 0 | 301,089
Gross amount of recognized liabilities for securities lending in offsetting disclosure in note 10 |  | 0
Amounts related to securities lending not included in offsetting disclosure in note 10 |  | 301,089
Fair value of cash collateral received on securities lending | 0 | 0
Fair value of non-cash collateral received on securities lending | $ 0 | 301,100
US government and government agencies |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 281,607
Corporate bonds |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 3,021
Equity securities |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 16,461
Overnight and continuous |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 161,799
Overnight and continuous | US government and government agencies |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 142,317
Overnight and continuous | Corporate bonds |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 3,021
Overnight and continuous | Equity securities |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 16,461
Less than 30 days |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 0
Less than 30 days | US government and government agencies |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 0
Less than 30 days | Corporate bonds |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 0
Less than 30 days | Equity securities |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 0
30 - 90 days |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 139,290
30 - 90 days | US government and government agencies |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 139,290
30 - 90 days | Corporate bonds |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 0
30 - 90 days | Equity securities |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 0
90 days or more |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 0
90 days or more | US government and government agencies |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 0
90 days or more | Corporate bonds |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | 0
90 days or more | Equity securities |  |
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items] |  |
Securities lending payable |  | $ 0

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- Definition The fair value of collateral received by the entity associated with securities borrowed that must be returned if the counterparty fulfills its obligations. It appears on the balance sheet as a liability and has a corresponding asset that appears on the balance sheet called Securities Received as Collateral. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.15) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 + Details
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- Definition Amount of secured borrowings in excess of (less than) the liability for repurchase agreements and securities lending transactions, before offset, included in offsetting disclosures. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 50 -Paragraph 7 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=109249958&loc=SL34722452-111729 + Details
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