Investments (Schedule of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	$ 55,513	$ 31,917	$ 146,045	$ 116,953
Investment expenses	(4,090)	(3,579)	(11,635)	(10,304)
Net investment income	51,423	28,338	134,410	106,649
Fixed maturity investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	39,959	37,023	122,056	96,753
Short term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	1,174	267	3,401	761
Equity investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	797	1,791	3,325	6,308
Private equity investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	4,572	(14,505)	(430)	1,333
Other
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	8,765	7,261	17,109	11,443
Cash and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	$ 246	$ 80	$ 584	$ 355