Investments in debt and equity securities - Gross Unrealized Gains and Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Gains	$ 7,297	$ 3,780
Losses	2,352	10,446
Municipal
Debt Securities, Available-for-sale [Line Items]
Gains	945	482
Losses	64	327
Corporate
Debt Securities, Available-for-sale [Line Items]
Gains	4,014	1,894
Losses	1,089	6,688
Foreign
Debt Securities, Available-for-sale [Line Items]
Gains	2,336	1,402
Losses	1,083	3,131
U.S. Treasury Bonds
Debt Securities, Available-for-sale [Line Items]
Gains	2	2
Losses	$ 116	$ 300

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=82897076&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=82897076&loc=d3e27161-111563

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