Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Net unrealized gains (losses) on investments	$ 199,712	$ 349,910
Derivatives designated as cash flow hedges
Investment [Line Items]
Net unrealized gains (losses) on investments	40,260	11,585
Fixed maturities | Available-for-sale Securities
Investment [Line Items]
Net unrealized gains (losses) on investments	149,188	322,358
Equity securities, available-for-sale | Available-for-sale Securities
Investment [Line Items]
Net unrealized gains (losses) on investments	(3,554)	619
Other investments
Investment [Line Items]
Net unrealized gains (losses) on investments	8,581	10,015
Securities Related to Other Than Temporary Impairments | Fixed maturities | Available-for-sale Securities
Investment [Line Items]
Net unrealized gains (losses) on investments	$ 5,237	$ 5,333