Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Accumulated deficit [Member]	Accumulated other comprehensive income (loss) [Member]	Treasury stock [Member]	Common Class A [Member]	Common Class A [Member] Common Stock [Member]	Common Class B [Member]	Common Class B [Member] Common Stock [Member]
Balance at Dec. 31, 2014	$ 262,332	$ (15,074)	$ 25,850	$ (11,011)		$ 259,383		$ 3,184
Net income (loss)	(3,143)	(3,143)
Unrealized investment gains (losses), net	(12,263)		(12,263)
Total comprehensive income (loss)	(15,406)
Balance at Dec. 31, 2015	246,926	(18,217)	13,587	$ (11,011)		259,383		3,184
Balance, shares at Dec. 31, 2015				(3,136)	52,216		1,002
Net income (loss)	1,969	1,969
Unrealized investment gains (losses), net	205		205
Total comprehensive income (loss)	2,174	1,969	205
Balance at Dec. 31, 2016	249,100	(16,248)	13,792	$ (11,011)		259,383		3,184
Balance, shares at Dec. 31, 2016				(3,136)	52,216		1,002
Net income (loss)	(38,127)	(38,127)
Unrealized investment gains (losses), net	12,540		12,540
Total comprehensive income (loss)	(25,587)	(38,127)	12,540
Balance at Dec. 31, 2017	$ 223,513	$ (54,375)	$ 26,332	$ (11,011)		$ 259,383		$ 3,184
Balance, shares at Dec. 31, 2017				(3,136)	52,216		1,002