Insurance (Guarantees Related to Annuity Contracts) (Details) - Variable Annuity Guarantees - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Guaranteed Death Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 4,881,902	$ 4,763,943
Separate account value	4,871,618	4,753,638
Net amount at risk	$ 11,875	$ 36,827
Average attained age of contractholders	67 years	66 years
Guaranteed Annuitization Benefits
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value	$ 4,054,825	$ 3,969,485
Separate account value	4,053,475	3,968,482
Net amount at risk	$ 185,679	$ 209,926
Average attained age of contractholders	65 years	65 years