Investments (Schedule of Net Realized and Unrealized Gains on Investments and Net Other-Than-Temporary Impairments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Gain (Loss) on Investments [Line Items]
Net realized and unrealized gains (losses) on investments	$ 59,870	$ (41,138)	$ 191,295	$ (26,101)
Fixed maturity investments
Gain (Loss) on Investments [Line Items]
Gross realized gains	20,383	9,160	60,794	39,364
Gross realized losses	(3,363)	(13,720)	(25,832)	(40,143)
Net realized gains (losses) on equity investments trading	17,020	(4,560)	34,962	(779)
Net realized gains (losses) on fixed maturity investments	(4,235)	10,208	125,501	(11,924)
Derivatives
Gain (Loss) on Investments [Line Items]
Net realized and unrealized gains (losses) on investments-related derivatives	1,727	(16,612)	(26,873)	(1,004)
Equity investments
Gain (Loss) on Investments [Line Items]
Net realized gains (losses) on equity investments trading	127	(114)	14,038	16,199
Net realized gains (losses) on fixed maturity investments	$ 45,231	$ (30,060)	$ 43,667	$ (28,593)