Investment information - Fair value option (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	$ 2,052,907	$ 1,954,895
Investments, fair value option - gross unrealized gains	37,956	36,601
Investments, fair value option - gross unrealized losses	(204,187)	(93,405)
Investments, fair value option	1,886,676	1,898,091
Equities, fair value through net income - cost	72,892	78,031
Equities, fair value through net income - gross unrealized gains	6,956	2,360
Equities, fair value through net income - gross unrealized losses	(17,404)	(15,053)
Equities, fair value through net income	62,444	65,338
Term loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	991,130	1,113,212
Investments, fair value option - gross unrealized gains	1,959	7,340
Investments, fair value option - gross unrealized losses	(117,529)	(58,618)
Investments, fair value option	875,560	1,061,934
Fixed maturities \| Corporate bonds
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	403,424	221,024
Investments, fair value option - gross unrealized gains	11,858	8,430
Investments, fair value option - gross unrealized losses	(36,589)	(15,100)
Investments, fair value option	378,693	214,354
Fixed maturities \| U.S. government and government agency bonds
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	584	1,963
Investments, fair value option - gross unrealized gains	11	1
Investments, fair value option - gross unrealized losses	0	(2)
Investments, fair value option	595	1,962
Fixed maturities \| Asset-backed securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	198,619	200,361
Investments, fair value option - gross unrealized gains	2,229	3,329
Investments, fair value option - gross unrealized losses	(42,923)	(12,953)
Investments, fair value option	157,925	190,737
Fixed maturities \| Mortgage-backed securities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	6,950	7,399
Investments, fair value option - gross unrealized gains	2,257	712
Investments, fair value option - gross unrealized losses	(43)	(405)
Investments, fair value option	9,164	7,706
Fixed maturities \| Non-U.S. government and government agency bonds
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	1,437	1,449
Investments, fair value option - gross unrealized gains	52	18
Investments, fair value option - gross unrealized losses	(107)	(11)
Investments, fair value option	1,382	1,456
Fixed maturities \| Municipal government and government agency bonds
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	251	380
Investments, fair value option - gross unrealized gains	0	0
Investments, fair value option - gross unrealized losses	0	(1)
Investments, fair value option	251	379
Short-term investments
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	370,976	325,542
Investments, fair value option - gross unrealized gains	597	3,817
Investments, fair value option - gross unrealized losses	(1,507)	(56)
Investments, fair value option	370,066	329,303
Other investments measured at net asset value (2)
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	28,673	28,672
Investments, fair value option - gross unrealized gains	5,469	2,264
Investments, fair value option - gross unrealized losses	0	(475)
Investments, fair value option	34,142	30,461
Equities
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, fair value option - cost or amortized cost	50,863	54,893
Investments, fair value option - gross unrealized gains	13,524	10,690
Investments, fair value option - gross unrealized losses	(5,489)	(5,784)
Investments, fair value option	$ 58,898	$ 59,799

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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Accumulated Unrealized Gains Fair Value Option

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Equity FV-NI Gross Accumulated Losses

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Certain fixed maturity securities, equity securities, term loans, short-term investments and other investments held at fair value under the fair value option afforded by accounting guidance regarding the fair value option for financial assets and liabilities.

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