Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Accumulated deficit [Member]	Accumulated other comprehensive income (loss) [Member]	Treasury Stock [Member]	Common Class A [Member] Common Stock [Member]	Common Class B [Member] Common Stock [Member]
Balance at Dec. 31, 2016	$ 249,100	$ (16,248)	$ 13,792	$ (11,011)	$ 259,383	$ 3,184
Net income (loss)	(38,127)	(38,127)	0	0	0	0
Unrealized investment gains (losses), net	12,540	0	12,540	0	0	0
Total comprehensive income (loss)	(25,587)	(38,127)	12,540	0	0	0
Balance at Dec. 31, 2017	223,513	(54,375)	26,332	(11,011)	259,383	3,184
Net income (loss)	(11,062)	(11,062)	0	0	0	0
Unrealized investment gains (losses), net	(28,498)	0	(28,498)	0	0	0
Unrealized gain from held-to-maturity securities transferred to available-for-sale, net	3,370	0	3,370	0	0	0
Total comprehensive income (loss)	(36,190)	(11,062)	(25,128)	0	0	0
Stock Issued During Period, Value, Stock Options Exercised	410	0	0	0	410	0
Balance at Dec. 31, 2018	187,733	(69,599)	5,366	(11,011)	259,793	3,184
Net income (loss)	(1,370)	(1,370)	0	0	0	0
Unrealized investment gains (losses), net	71,751	0	71,751	0	0	0
Total comprehensive income (loss)	70,381	(1,370)	71,751	0	0	0
Stock Issued During Period, Value, Stock Options Exercised	1,722	0	0	0	1,722	0
Balance at Dec. 31, 2019	$ 259,836	$ (70,969)	$ 77,117	$ (11,011)	$ 261,515	$ 3,184