Unsecured Debt - Unsecured Private Placement Bonds (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Senior notes	$ 200,000	$ 200,000
Unsecured Bonds 4.27%
Debt Instrument [Line Items]
Senior notes	$ 100,000	100,000
Coupon Rate	4.27%
Unsecured Bonds 4.30%
Debt Instrument [Line Items]
Senior notes	$ 50,000	50,000
Coupon Rate	4.30%
Unsecured Bonds 4.37%
Debt Instrument [Line Items]
Senior notes	$ 50,000	$ 50,000
Coupon Rate	4.37%

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
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+ References

No definition available.

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+ 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 210.7-03.16(a))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

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-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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