Significant Accounting Policies (Annuity Deposits (Net of Coinsurance), By Product Type) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) NMOs	Dec. 31, 2017 USD ($) NMOs	Dec. 31, 2016 USD ($) NMOs
Product Information [Line Items]
Fixed index annuities	$ 3,898,366	$ 3,668,121	$ 5,035,818
Annual reset fixed rate annuities	46,744	74,572	63,582
Multi-year fixed rate annuities	22,818	22,291	256,894
Single premium immediate annuities (SPIA)	23,813	24,946	35,851
Annuity deposits, net of coinsurance	$ 3,991,741	$ 3,789,930	$ 5,392,145
Customer Concentration Risk
Product Information [Line Items]
National marketing organizations, number of organizations accounting for more than 10% of annuity deposits collected | NMOs	2	2	1
Customer Concentration Risk | National Marketing Organization, Greater than 10%, NMO 1
Product Information [Line Items]
National marketing organizations, percent of annuity deposits collected individually	20.00%	14.00%	15.00%
Customer Concentration Risk | National Marketing Organization, Greater than 10%, NMO 2
Product Information [Line Items]
National marketing organizations, percent of annuity deposits collected individually	14.00%	10.00%