Investments - Schedule of Available-for-sale Securities in Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Less than or equal to One Year, Fair value	$ 282,828	$ 16,603
Less than or equal to One Year, Gross unrealized losses	$ (1,790)	$ (60)
Less than or Equal to One Year, Number of Securities \| security	577	49
More Than One Year, Fair value	$ 9,764	$ 18,929
More than One Year, Gross unrealized loss	$ (2,209)	$ (2,099)
More than One Year, Number of securities \| security	28	11
U.S. Treasury securities and obligations of U.S. government authorities and agencies
Debt Securities, Available-for-sale [Line Items]
Less than or equal to One Year, Fair value	$ 188,046	$ 15,323
Less than or equal to One Year, Gross unrealized losses	$ (1,059)	$ (58)
Less than or Equal to One Year, Number of Securities \| security	267	41
More Than One Year, Fair value	$ 6,094	$ 2
More than One Year, Gross unrealized loss	$ (162)	$ 0
More than One Year, Number of securities \| security	20	2
Obligations of state and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Less than or equal to One Year, Fair value	$ 12,303	$ 379
Less than or equal to One Year, Gross unrealized losses	$ (203)	$ (1)
Less than or Equal to One Year, Number of Securities \| security	41	5
More Than One Year, Fair value	$ 279	$ 0
More than One Year, Gross unrealized loss	$ (11)	$ 0
More than One Year, Number of securities \| security	3	0
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Less than or equal to One Year, Fair value	$ 76,400	$ 901
Less than or equal to One Year, Gross unrealized losses	$ (483)	$ (1)
Less than or Equal to One Year, Number of Securities \| security	240	3
More Than One Year, Fair value	$ 0	$ 0
More than One Year, Gross unrealized loss	$ 0	$ 0
More than One Year, Number of securities \| security	0	0
Asset backed securities
Debt Securities, Available-for-sale [Line Items]
Less than or equal to One Year, Fair value	$ 4,195	$ 0
Less than or equal to One Year, Gross unrealized losses	$ (11)	$ 0
Less than or Equal to One Year, Number of Securities \| security	23	0
More Than One Year, Fair value	$ 3,391	$ 18,927
More than One Year, Gross unrealized loss	$ (2,036)	$ (2,099)
More than One Year, Number of securities \| security	5	9
Obligations of foreign governments
Debt Securities, Available-for-sale [Line Items]
Less than or equal to One Year, Fair value	$ 1,884
Less than or equal to One Year, Gross unrealized losses	$ (34)
Less than or Equal to One Year, Number of Securities \| security	6
More Than One Year, Fair value	$ 0
More than One Year, Gross unrealized loss	$ 0
More than One Year, Number of securities \| security	0

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27337-111563

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without an allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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