Fair Value - Rollforward of Level 3 assets and liabilities (Details) - Recurring - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Contingent consideration liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ (1,250)	$ (7,825)	$ (7,998)	$ (66,665)
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	(79)	(72)	(1,410)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	0	0
Issuances		0	0	0	(548)
Sales		0	0	0	0
Settlements		620	560	7,440	61,279
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		(630)	(7,344)	(630)	(7,344)
Available for sale | Structured securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	[2]	3,450	290	5,216	313
Total gains or (losses) (realized/unrealized) - included in earnings	[1],[2]	(75)	0	(130)	1,757
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	[2]	191	0	(118)	5
Purchases, issuances, sales and settlements
Purchases	[2]	0	0	0	0
Issuances	[2]	0	0	0	0
Sales	[2]	0	0	0	(1,757)
Settlements	[2]	(11)	(18)	(1,413)	(46)
Transfers in and/or out of Level 3	[2]	0	5,449	0	5,449
Balance at end of period	[2]	3,555	5,721	3,555	5,721
Available for sale | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		857	7,642	8,851	8,141
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(5,872)	0	(5,865)	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		6,936	(301)	397	(317)
Purchases, issuances, sales and settlements
Purchases		0	0	0	429
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	(456)	(1,462)	(1,368)
Transfers in and/or out of Level 3		(1,908)	1,860	(1,908)	1,860
Balance at end of period		13	8,745	13	8,745
Fair value option | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		998	26,103	932	5,758
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(34)	(1,227)	(34)	(1,566)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	66	0
Issuances		0	0	0	0
Sales		0	(2,097)	0	(5,332)
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	0	0	23,919
Balance at end of period		964	22,779	964	22,779
Fair value option | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		46,453	95,273	68,817	62,705
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	885	(411)	(129)	(11,727)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		22,436	3,713	22,460	3,713
Issuances		0	0	0	0
Sales		(3,588)	(80)	(27,946)	(228)
Settlements		0	0	0	(600)
Transfers in and/or out of Level 3		0	(13,052)	2,984	31,580
Balance at end of period		66,186	85,443	66,186	85,443
Fair value option | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		61,447	56,145	58,094	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	2,076	127	5,429	127
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	0	0
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	0	0	56,145
Balance at end of period		63,523	56,272	63,523	56,272
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		51,981	51,212	55,889	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(946)	(26)	7,132	(26)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	12,119	3,464	12,119
Issuances		0	0	0	0
Sales		(8,349)	(27,982)	(23,799)	(27,982)
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	0	0	51,212
Balance at end of period		$ 42,686	$ 35,323	$ 42,686	$ 35,323

[1] Gains or losses were included in net realized gains (losses).

[2] Includes asset backed securities, mortgage backed securities and commercial mortgage backed securities.