Investment Information - Net realized gains and losses (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net realized gains and losses:
Available for sale securities, gross gains on investment sales		$ 76,730	$ 74,695	$ 145,905	$ 182,514
Available for sale securities, gross losses on investment sales		(52,619)	(43,293)	(113,981)	(106,424)
Derivative instruments	[1]	(4,770)	20,334	(13,951)	41,066
Other	[2]	(14,056)	(15,066)	(19,873)	(20,895)
Net realized gains (losses)		21,735	68,218	55,888	105,542
Fixed maturities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		9,656	18,632	30,197	18,299
Other investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		637	13,136	17,885	(8,412)
Equity securities
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		2,829	401	6,374	437
Short-term investments
Net realized gains and losses:
Change in fair value of assets and liabilities accounted for using the fair value option		$ 3,328	$ (621)	$ 3,332	$ (1,043)

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

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