Borrowings - Components of Borrowings (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Debt and capital lease obligations	$ 200,000	$ 200,000
Senior notes \| Series C
Debt Instrument [Line Items]
Debt and capital lease obligations	$ 90,000	$ 90,000
Interest Rate Per Annum	5.82%	5.82%
Senior notes \| Series D
Debt Instrument [Line Items]
Debt and capital lease obligations	$ 60,000	$ 60,000
Interest Rate Per Annum	4.29%	4.29%
Senior notes \| Series E
Debt Instrument [Line Items]
Debt and capital lease obligations	$ 50,000	$ 50,000
Interest Rate Per Annum	4.53%	4.53%
Revolving credit agreement
Debt Instrument [Line Items]
Debt and capital lease obligations	$ 0	$ 0

Amount of short-term and long-term debt and lease obligation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13,16)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: 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)
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

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

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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))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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