Unaudited Interim Statements of Financial Position (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Fixed Maturities, Available-for-sale, Amortized Cost	$ 13,264,558	$ 12,465,746
Fixed Maturities, Available-for-sale, allowance for credit losses	186
Fixed maturities, trading, amortized cost	347,115	349,428
Equity securities, at cost	74,271	63,647
Commercial mortgage and other loans, allowance for credit losses	6,282	2,663
Other invested assets, at fair value	$ 28,761	$ 10,492
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