Fair Value - Rollforward of Level 3 assets and liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 54,238	$ 72,666	$ 54,633	$ 73,868
Total gains or (losses) (realized/unrealized) - included in earnings	3,708	(1,137)	4,672	(2,339)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0	0	0	0
Purchases, issuances, sales and settlements
Purchases	4,935	776	4,935	776
Issuances	0	0	0	0
Sales	(26,242)	0	(26,242)	0
Settlements	(69)	(5,789)	(1,428)	(5,789)
Transfers in and/or out of Level 3	0	0	0	0
Balance at end of period	36,570	66,516	36,570	66,516
Contingent consideration liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	(125,544)	(100,710)	(122,350)	(96,048)
Total gains or (losses) (realized/unrealized) - included in earnings	(3,441)	(10,923)	(7,087)	(16,121)
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0	(37)	0	(37)
Purchases, issuances, sales and settlements
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	71,739	0	(72,191)	536
Transfers in and/or out of Level 3	0	0	0	0
Balance at end of period	(57,246)	(111,670)	(57,246)	(111,670)
Available for sale | Asset backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	10,637	57,500	11,289	57,500
Total gains or (losses) (realized/unrealized) - included in earnings	3,072	(2,500)	3,779	(2,500)
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	(13,640)	0	(13,640)	0
Settlements	(69)	(5,789)	(1,428)	(5,789)
Transfers in and/or out of Level 3	0	0	0	0
Balance at end of period	0	49,211	0	49,211
Fair value option | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	18,601	15,166	18,344	16,368
Total gains or (losses) (realized/unrealized) - included in earnings	636	1,363	893	161
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0	0	0	0
Purchases, issuances, sales and settlements
Purchases	4,935	776	4,935	776
Issuances	0	0	0	0
Sales	(12,602)	0	(12,602)	0
Settlements	0	0	0	0
Transfers in and/or out of Level 3	0	0	0	0
Balance at end of period	11,570	17,305	11,570	17,305
Fair value option | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	25,000	0	25,000	0
Total gains or (losses) (realized/unrealized) - included in earnings	0	0	0	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	0	0
Balance at end of period	$ 25,000	$ 0	$ 25,000	$ 0