Fair Value - Rollforward of Level 3 assets and liabilities (Details) - Recurring - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Contingent consideration liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ (7,825)	$ (63,930)	$ (66,665)	$ (60,996)
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(79)	(1,711)	(1,410)	(4,645)
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	(548)	0
Sales		0	0	0	0
Settlements		560	0	(61,279)	0
Transfers in and/or out of Level 3		0	0	0	0
Balance at end of period		(7,344)	(65,641)	(7,344)	(65,641)
Available for sale | Structured securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	[2]	290	376	313	5,927
Total gains or (losses) (realized/unrealized) - included in earnings	[1],[2]	0	0	1,757	4
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	[2]	0	2	5	(6)
Purchases, issuances, sales and settlements
Purchases	[2]	0	0	0	0
Issuances	[2]	0	0	0	0
Sales	[2]	0	0	(1,757)	(5,003)
Settlements	[2]	(18)	(33)	(46)	(577)
Transfers in and/or out of Level 3	[2]	5,449	0	5,449	0
Balance at end of period	[2]	5,721	345	5,721	345
Available for sale | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		7,642	8,773	8,141	9,460
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	0	(1)	0	(1)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		(301)	(32)	(317)	(200)
Purchases, issuances, sales and settlements
Purchases		0	0	429	393
Issuances		0	0	0	0
Sales		0	0	0	0
Settlements		(456)	(456)	(1,368)	(1,368)
Transfers in and/or out of Level 3		1,860	0	1,860	0
Balance at end of period		8,745	8,284	8,745	8,284
Fair value option | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		26,103	11,335	5,758	12,217
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(1,227)	(503)	(1,566)	(1,115)
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		(2,097)	0	(5,332)	0
Settlements		0	(1,226)	0	(1,496)
Transfers in and/or out of Level 3		0	0	23,919	0
Balance at end of period		22,779	9,606	22,779	9,606
Fair value option | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		95,273	58,214	62,705	59,167
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(411)	(1,459)	(11,727)	(1,838)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		3,713	6,250	3,713	6,250
Issuances		0	0	0	0
Sales		(80)	(74)	(228)	(148)
Settlements		0	0	(600)	(500)
Transfers in and/or out of Level 3		(13,052)	0	31,580	0
Balance at end of period		85,443	62,931	85,443	62,931
Fair value option | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		56,145	0	0	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	127	0	127	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	0	56,145	0
Balance at end of period		56,272	0	56,272	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		51,212	0	0	0
Total gains or (losses) (realized/unrealized) - included in earnings	[1]	(26)	0	(26)	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income		0	0	0	0
Purchases, issuances, sales and settlements
Purchases		12,119	0	12,119	0
Issuances		0	0	0	0
Sales		(27,982)	0	(27,982)	0
Settlements		0	0	0	0
Transfers in and/or out of Level 3		0	0	51,212	0
Balance at end of period		$ 35,323	$ 0	$ 35,323	$ 0

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

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