Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Gain (Loss) on Investments [Line Items]
Net unrealized gains (losses) on investments	$ 459,217	$ 107,460
Derivatives designated as cash flow hedges
Gain (Loss) on Investments [Line Items]
Net unrealized gains (losses) on investments	14,090	14,847
Fixed maturities
Gain (Loss) on Investments [Line Items]
Net unrealized gains (losses) on investments	444,644	90,637
Fixed maturities | Securities Related to Other Than Temporary Impairments
Gain (Loss) on Investments [Line Items]
Net unrealized gains (losses) on investments	(788)	9
Equity securities, available-for-sale
Gain (Loss) on Investments [Line Items]
Net unrealized gains (losses) on investments	4	3
Affiliated notes
Gain (Loss) on Investments [Line Items]
Net unrealized gains (losses) on investments	1,574	1,660
Other investments
Gain (Loss) on Investments [Line Items]
Net unrealized gains (losses) on investments	$ (307)	$ 304