Fair Value - Rollforward of Level 3 assets and liabilities (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 549,990	$ 477,956
Total gains or (losses) (realized/unrealized) - included in earnings	8,585	6,627
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	(2,196)	224
Purchases, issuances, sales and settlements
Purchases	40,110	46,654
Issuances	0	0
Sales	(68,209)	0
Settlements	(4,799)	(68,859)
Transfers in and/or out of Level 3	0	0
Balance at end of period	523,481	462,602
Contingent consideration liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0	0
Total gains or (losses) (realized/unrealized) - included in earnings	(1,394)	0
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0	0
Purchases, issuances, sales and settlements
Purchases	0	0
Issuances	(41,762)	0
Sales	0	0
Settlements	0	0
Transfers in and/or out of Level 3	0	0
Balance at end of period	(43,156)	0
Available for sale | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	2,045	98,404
Total gains or (losses) (realized/unrealized) - included in earnings	0	1,492
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0	(1,688)
Purchases, issuances, sales and settlements
Purchases	0	0
Issuances	0	0
Sales	(2,045)	0
Settlements	0	(910)
Transfers in and/or out of Level 3	0	0
Balance at end of period	0	97,298
Available for sale | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	170,420	184,202
Total gains or (losses) (realized/unrealized) - included in earnings	2,275	4,762
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	(2,196)	1,912
Purchases, issuances, sales and settlements
Purchases	0	5,000
Issuances	0	0
Sales	(66,164)	0
Settlements	0	(9,942)
Transfers in and/or out of Level 3	0	0
Balance at end of period	104,335	185,934
Fair value option | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	377,525	195,350
Total gains or (losses) (realized/unrealized) - included in earnings	6,310	373
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0	0
Purchases, issuances, sales and settlements
Purchases	40,110	41,654
Issuances	0	0
Sales	0	0
Settlements	(4,799)	(58,007)
Transfers in and/or out of Level 3	0	0
Balance at end of period	$ 419,146	$ 179,370