Consolidated Statements of Stockholder's Equity Statement - USD ($) $ in Thousands	Total	Accumulated deficit [Member]	Accumulated other comprehensive income [Member]	Treasury stock [Member]	Common Stock Class A [Member] Common stock [Member]	Common Stock Class B [Member] Common stock [Member]
Balance at Dec. 31, 2017	$ 223,513	$ (54,375)	$ 26,332	$ (11,011)	$ 259,383	$ 3,184
Net income (loss)	37	37	0	0	0	0
Unrealized investment gains (losses), net	(14,104)	0	(14,104)	0	0	0
Comprehensive income (loss)	(14,067)	37	(14,104)	0	0	0
Balance at Mar. 31, 2018	209,446	(58,500)	16,390	(11,011)	259,383	3,184
Balance at Dec. 31, 2018	187,733	(69,599)	5,366	(11,011)	259,793	3,184
Net income (loss)	(3,802)	(3,802)	0	0	0	0
Unrealized investment gains (losses), net	26,880	0	26,880	0	0	0
Comprehensive income (loss)	23,078	(3,802)	26,880	0	0	0
Stock-based compensation	1,083	0	0	0	1,083	0
Balance at Mar. 31, 2019	$ 211,894	$ (73,401)	$ 32,246	$ (11,011)	$ 260,876	$ 3,184