BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Fixed maturity available-for-sale securities, amortized cost	$ 1,354,397	$ 1,383,787
Equity available-for-sale securities, cost	$ 31,264	$ 31,264
Common stock, par value	$ 10	$ 10
Common stock, shares authorized	1,000,000	1,000,000
Common stock, shares issued	250,000	250,000
Common stock, shares outstanding	250,000	250,000