Fair Value - Rollforward of Level 3 assets and liabilities (Details) - Recurring - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Contingent consideration liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ (7,967)	$ (68,121)	$ (7,998)	$ (66,665)
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(18)	(423)	(72)	(1,331)
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		6,735	60,719	6,820	60,719
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		(1,250)	(7,825)	(1,250)	(7,825)
Available for sale | Structured securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	[2]	3,846	302	5,216	313
Total gains or (losses) (realized/unrealized) - included in earnings	[1],[2]	(64)	0	(55)	1,757
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	[2]	(287)	1	(309)	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]	(45)	(13)	(1,402)	(28)
Transfers in and/or out of Level 3	[2]	0	0	0	0
Balance at end of period	[2]	3,450	290	3,450	290
Available for sale | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		1,980	7,567	8,851	8,141
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	0	7	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		(1,123)	102	(6,539)	(16)
Purchases, issuances, sales and settlements
Purchases		0	429	0	429
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		0	(456)	(1,462)	(912)
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		857	7,642	857	7,642
Fair value option | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		965	2,233	932	5,758
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	(49)	0	(339)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		33	0	66	0
Issuances		0	0	0	0
Sales		0	0	0	(3,235)
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	23,919	0	23,919
Balance at end of period		998	26,103	998	26,103
Fair value option | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		54,620	62,329	68,817	62,705
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(987)	(11,614)	(1,014)	(11,316)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		3	0	24	0
Issuances		0	0	0	0
Sales		(7,183)	(74)	(24,358)	(148)
Settlements		0	0	0	(600)
Transfers in and/or out of Level 3		0	44,632	2,984	44,632
Balance at end of period		46,453	95,273	46,453	95,273
Fair value option | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		60,015	0	58,094	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	1,432	0	3,353	0
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	56,145	0	56,145
Balance at end of period		61,447	56,145	61,447	56,145
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		55,632	0	55,889	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	11,799	0	8,078	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		0	0	3,464	0
Issuances		0	0	0	0
Sales		(15,450)	0	(15,450)	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	51,212	0	51,212
Balance at end of period		$ 51,981	$ 51,212	$ 51,981	$ 51,212

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

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