Fair Value - Rollforward of Level 3 assets and liabilities (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Contingent consideration liability
Level 3 liabilities rollforward
Balance at beginning of year		$ (66,665)	$ (60,996)
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(1,478)	(5,669)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		(548)	0
Sales		0	0
Settlements		60,693	0
Transfers in and/or out of Level 3		0	0
Balance at end of year		(7,998)	(66,665)
Equity securities
Level 3 assets rollforward
Balance at beginning of year		0	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(3,418)	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		36,077	0
Issuances		0	0
Sales		(27,982)	0
Settlements		0	0
Transfers in and/or out of Level 3		51,212	0
Balance at end of year		55,889	0
Available for sale | Asset backed securities
Level 3 assets rollforward
Balance at beginning of year		313	5,927
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	1,760	4
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		3	(11)
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		(1,757)	(5,003)
Settlements		(552)	(604)
Transfers in and/or out of Level 3		5,449	0
Balance at end of year		5,216	313
Available for sale | Corporate bonds
Level 3 assets rollforward
Balance at beginning of year		8,141	9,460
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	2	(1)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		(267)	(296)
Purchases, issuances, sales and settlements
Purchases		881	802
Issuances		0	0
Sales		0	0
Settlements		(1,766)	(1,824)
Transfers in and/or out of Level 3		1,860	0
Balance at end of year		8,851	8,141
Fair value option | Corporate bonds
Level 3 assets rollforward
Balance at beginning of year		5,758	12,217
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(162)	(334)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		(28,583)	0
Settlements		0	(6,125)
Transfers in and/or out of Level 3		23,919	0
Balance at end of year		932	5,758
Fair value option | Other investments
Level 3 assets rollforward
Balance at beginning of year		62,705	59,167
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(8,119)	(1,416)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		3,746	6,250
Issuances		0	0
Sales		(20,495)	(296)
Settlements		(600)	(1,000)
Transfers in and/or out of Level 3		31,580	0
Balance at end of year		68,817	62,705
Fair value option | Equity securities
Level 3 assets rollforward
Balance at beginning of year		0	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	1,949	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		0	0
Settlements		0	0
Transfers in and/or out of Level 3		56,145	0
Balance at end of year		$ 58,094	$ 0

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