Certain Long-Duration Contracts With Guarantees (Summary of the Changes in General Account Liabilities for Guarantees on Variable Contracts) (Details) - Variable Annuity Contracts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Liabilities for Guarantee Benefits, Beginning Balance	$ 3,387,128	$ 989,375	$ 2,039,178
Incurred guarantee benefits	60,217	2,424,215	(1,029,750)
Paid guarantee benefits	(29,751)	(26,633)	(28,254)
Changes in unrealized investment gains and losses	(3,776)	171	8,201
Liabilities for Guarantee Benefits, Ending Balance	3,413,818	3,387,128	989,375
GMDB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Liabilities for Guarantee Benefits, Beginning Balance	255,613	199,870	222,527
Incurred guarantee benefits	43,167	81,524	(3,191)
Paid guarantee benefits	(29,240)	(25,909)	(27,507)
Changes in unrealized investment gains and losses	(3,663)	128	8,041
Liabilities for Guarantee Benefits, Ending Balance	265,877	255,613	199,870
GMAB/GMWB/ GMIWB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Liabilities for Guarantee Benefits, Beginning Balance	3,112,411	778,226	1,793,135
Incurred guarantee benefits	21,666	2,334,185	(1,014,909)
Paid guarantee benefits	0	0	0
Changes in unrealized investment gains and losses	0	0	0
Liabilities for Guarantee Benefits, Ending Balance	3,134,077	3,112,411	778,226
GMIB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Liabilities for Guarantee Benefits, Beginning Balance	19,104	11,279	23,516
Incurred guarantee benefits	(4,616)	8,506	(11,650)
Paid guarantee benefits	(511)	(724)	(747)
Changes in unrealized investment gains and losses	(113)	43	160
Liabilities for Guarantee Benefits, Ending Balance	$ 13,864	$ 19,104	$ 11,279