Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Class A common stock	Class B common stock	Class U common stock	Common Stock Class A common stock	Common Stock Class B common stock	Common Stock Class U common stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance, Beginning at Dec. 31, 2018	$ 332,732				$ 6	$ 2	$ 1		$ 862,299	$ (528,164)	$ (1,412)
Balance, Beginning, Shares at Dec. 31, 2018					63,210,531	14,927,613	9,352,729
Tax payments related to shares withheld for share-based compensation plans	(42)								(42)
Tax payments related to shares withheld for share-based compensation plans, shares					25,059
Stock-based compensation expense	800								800
Repurchase of Class A common stock	(7,706)								(7,706)
Repurchase of Class A common stock, Shares					(2,098,443)			2,098,443
Retirement of treasury stock, Shares								(2,098,443)
Dividends paid	(4,271)								(4,271)
Change in fair value of marketable securities	763										763
Foreign currency translation gain (loss)	30										30
Net income (loss)	1,424									1,424
Balance, Ending at Mar. 31, 2019	323,730				$ 6	$ 2	$ 1		851,080	(526,740)	(619)
Balance, Ending, Shares at Mar. 31, 2019					61,137,147	14,927,613	9,352,729
Balance, Beginning at Dec. 31, 2019	288,172				$ 6	$ 2	$ 1		836,170	(547,876)	(131)
Balance, Beginning, Shares at Dec. 31, 2019		60,074,698	14,927,613	9,352,729	60,074,698	14,927,613	9,352,729
Stock-based compensation expense	789								789
Repurchase of Class A common stock	(525)	$ (500)							(525)
Repurchase of Class A common stock, Shares		(300,000)			(259,500)			259,500
Retirement of treasury stock, Shares								(259,500)
Dividends paid	(4,218)								(4,218)
Change in fair value of marketable securities	(223)										(223)
Foreign currency translation gain (loss)	(166)										(166)
Net income (loss)	(35,592)									(35,592)
Balance, Ending at Mar. 31, 2020	$ 248,237				$ 6	$ 2	$ 1		$ 832,216	$ (583,468)	$ (520)
Balance, Ending, Shares at Mar. 31, 2020		59,815,198	14,927,613	9,352,729	59,815,198	14,927,613	9,352,729