Consolidated Statements of Stockholder's Equity Statement - USD ($)	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, 2016	$ 249,100,000	$ (16,248,000)	$ 13,792,000	$ (11,011,000)	$ 259,383,000	$ 3,184,000
Net income (loss)	6,077,000	6,077,000	0	0	0	0
Unrealized investment gains (losses), net	9,044,000	0	9,044,000	0	0	0
Comprehensive income (loss)	15,121,000	6,077,000	9,044,000	0	0	0
Stock-based compensation	0
Balance at Sep. 30, 2017	264,221,000	(10,171,000)	22,836,000	(11,011,000)	259,383,000	3,184,000
Accounting standards adopted January 1, 2018	0	(4,162,000)	4,162,000	0	0	0
Balance at January 1, 2018	223,513,000	(58,537,000)	30,494,000	(11,011,000)	259,383,000	3,184,000
Balance at Dec. 31, 2017	223,513,000	(54,375,000)	26,332,000	(11,011,000)	259,383,000	3,184,000
Net income (loss)	(17,275,000)	(17,275,000)	0	0	0	0
Unrealized investment gains (losses), net	(26,629,000)	0	(26,629,000)	0	0	0
Unrealized gain from held-to-maturity securities transferred to available-for-sale, net	820,000	0	820,000	0	0	0
Comprehensive income (loss)	(43,084,000)	(17,275,000)	(25,809,000)	0	0	0
Stock-based compensation	310,000	0	0	0	310,000	0
Balance at Sep. 30, 2018	$ 180,739,000	$ (75,812,000)	$ 4,685,000	$ (11,011,000)	$ 259,693,000	$ 3,184,000