Unaudited Interim Statements of Financial Position (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, amortized cost	$ 11,736,191	$ 10,186,465
Fixed maturities, trading, amortized cost	327,977	294,549
Equity securities, at cost	23,456	18,765
Other invested assets, at fair value	$ 8,200	$ 50,945
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