Investment Information - Net realized gains and losses (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net realized gains and losses:
Available for sale securities, gross gains on investment sales		$ 66,565	$ 84,451	$ 212,470	$ 266,965
Available for sale securities, gross losses on investment sales		(39,015)	(22,985)	(152,996)	(129,409)
Derivative instruments	[1]	4,298	(16,964)	(9,653)	24,102
Other	[2]	(782)	(10,858)	(20,655)	(31,753)
Net realized gains (losses)		66,275	125,105	122,163	230,647
Fixed maturities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		4,035	43,935	34,232	62,234
Other investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		24,264	46,428	42,149	38,016
Equity securities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		10,230	(52)	16,604	385
Short-term investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		$ (3,320)	$ 1,150	$ 12	$ 107

[1] See Note 9 for information on the Company’s derivative instruments.

[2] Includes the re-measurement of contingent consideration liability amounts.