Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Accumulated deficit [Member]	Accumulated deficit [Member] Cumulative Effect, Period of Adoption, Adjustment	Accumulated other comprehensive income (loss) [Member]	Accumulated other comprehensive income (loss) [Member] Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock [Member]	Treasury Stock [Member] Cumulative Effect, Period of Adoption, Adjustment	Common Class A [Member] Common Stock [Member]	Common Class A [Member] Common Stock [Member] Cumulative Effect, Period of Adoption, Adjustment	Common Class B [Member] Common Stock [Member]	Common Class B [Member] Common Stock [Member] Cumulative Effect, Period of Adoption, Adjustment
Balance at Dec. 31, 2017	$ 223,513		$ (54,375)		$ 26,332		$ (11,011)		$ 259,383		$ 3,184
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
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 0		$ (4,162)		$ 4,162		$ 0		$ 0		$ 0
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
Net income (loss)	(10,988)		(10,988)		0		0		0		0
Unrealized investment gains (losses), net	51,138		0		51,138		0		0		0
Total comprehensive income (loss)	40,150		(10,988)		51,138		0		0		0
Stock Issued During Period, Value, Stock Options Exercised	1,354		0		0		0		1,354		0
Balance at Dec. 31, 2020	$ 300,945		$ (82,352)		$ 128,255		$ (11,011)		$ 262,869		$ 3,184