Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Amortized cost	$ 187,035	$ 183,432
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	4,010,150	4,010,150
Common stock, shares issued	3,530,150	0
Common stock, shares outstanding	3,530,150	0