Unaudited Interim Statements of Financial Position (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, amortized cost	$ 9,871,624	$ 10,145,266
Fixed maturities, trading, amortized cost	271,233	161,393
Equity securities, at cost	9,314	11,614
Other invested assets, at fair value	$ 7,567	$ 151,481
Common stock, par value (in dollars per share)	$ 100	$ 100
Common stock, shares authorized	25,000	25,000
Common stock, shares issued	25,000	25,000
Common stock, shares outstanding	25,000	25,000