Mortgage Loans on Real Estate (Schedule of Financing Receivables Past Due) (Details) - Commercial Real Estate Portfolio Segment - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Commercial mortgage loans, past due	$ 0	$ 0
Commercial mortgage loans, current	3,684,149	3,457,972
Commercial mortgage loans, collateral dependent receivables	4,252	0
Amortized cost	3,688,401	3,457,972
30 to 59 Days
Financing Receivable, Past Due [Line Items]
Commercial mortgage loans, past due	0	0
60 to 89 Days
Financing Receivable, Past Due [Line Items]
Commercial mortgage loans, past due	0	0
90 Days and Over
Financing Receivable, Past Due [Line Items]
Commercial mortgage loans, past due	$ 0	$ 0

Amount, after fee received for commitment to originate or purchase, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5074-111524

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 55
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Reference 4: http://www.xbrl.org/2003/role/exampleRef
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-Name Accounting Standards Codification
-Topic 326
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-Section 55
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-URI http://asc.fasb.org/extlink&oid=118955255&loc=SL82922355-210448

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