Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investment [Line Items]
Net unrealized gains (losses) on investments	$ 117,033	$ 349,910	$ 127,651
Other investments
Investment [Line Items]
Net unrealized gains (losses) on investments	6,272	10,015	19,680
Available-for-sale Securities | Fixed maturities, available-for-sale
Investment [Line Items]
Net unrealized gains (losses) on investments	59,930	322,358	107,970
Available-for-sale Securities | Equity securities, available-for-sale
Investment [Line Items]
Net unrealized gains (losses) on investments	(2,636)	619	204
Fixed maturity securities on which an OTTI loss has been recognized | Available-for-sale Securities | Fixed maturities, available-for-sale
Investment [Line Items]
Net unrealized gains (losses) on investments	5,196	5,333	4,498
Derivatives designated as cash flow hedges
Investment [Line Items]
Net unrealized gains (losses) on investments	$ 48,271	$ 11,585	$ (4,701)