Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Amortized cost	$ 192,573	$ 187,035
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	4,010,250	4,010,250
Common stock, shares issued	3,530,250	3,530,150
Common stock, shares outstanding	3,530,250	3,530,150