Investments in debt and equity securities - Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Gains	$ 32,165	$ 14,162
Losses	191	1,089
Municipal
Debt Securities, Available-for-sale [Line Items]
Gains	2,465	1,649
Losses	0	2
Corporate
Debt Securities, Available-for-sale [Line Items]
Gains	19,594	10,091
Losses	106	23
Foreign
Debt Securities, Available-for-sale [Line Items]
Gains	10,024	2,362
Losses	61	1,023
U.S. Treasury Bonds
Debt Securities, Available-for-sale [Line Items]
Gains	82	60
Losses	$ 24	$ 41

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

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- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

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