Investments (Schedule of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	$ 58,017	$ 32,749
Investment expenses	(3,692)	(3,886)
Net investment income	54,325	28,863
Fixed maturity investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	43,419	36,006
Short term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	1,724	1,000
Equity investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	811	1,663
Private equity investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	7,802	(9,358)
Other
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	4,072	3,309
Cash and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income before investment expenses	$ 189	$ 129