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, 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
Foreign currency translation gain (loss)	(288)
Net income (loss)	(14,855)
Balance, Ending at Jun. 30, 2019	302,921				$ 6	$ 2	$ 1		846,345	(543,019)	(414)
Balance, Ending, Shares at Jun. 30, 2019					60,718,613	14,927,613	9,352,729
Balance, Beginning at Mar. 31, 2019	323,730				$ 6	$ 2	$ 1		851,080	(526,740)	(619)
Balance, Beginning, Shares at Mar. 31, 2019					61,137,147	14,927,613	9,352,729
Issuance of common stock upon exercise of stock options or awards of restricted stock units, Shares					20,000
Stock-based compensation expense	836								836
Repurchase of Class A common stock	(1,302)				$ 0				(1,302)
Repurchase of Class A common stock, Shares					(438,534)			438,534
Retirement of treasury stock, Shares								(438,534)
Dividends paid	(4,269)								(4,269)
Change in fair value of marketable securities	523										523
Foreign currency translation gain (loss)	(318)										(318)
Net income (loss)	(16,279)									(16,279)
Balance, Ending at Jun. 30, 2019	302,921				$ 6	$ 2	$ 1		846,345	(543,019)	(414)
Balance, Ending, Shares at Jun. 30, 2019					60,718,613	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)								(525)
Repurchase of Class A common stock, Shares					(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
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
Foreign currency translation gain (loss)	301
Net income (loss)	(33,254)
Balance, Ending at Jun. 30, 2020	250,260				$ 6	$ 2	$ 1		830,900	(581,130)	481
Balance, Ending, Shares at Jun. 30, 2020		59,905,386	14,927,613	9,352,729	59,905,386	14,927,613	9,352,729
Balance, Beginning at Mar. 31, 2020	248,237				$ 6	$ 2	$ 1		832,216	(583,468)	(520)
Balance, Beginning, Shares at Mar. 31, 2020					59,815,198	14,927,613	9,352,729
Issuance of common stock upon exercise of stock options or awards of restricted stock units	(15)								(15)
Issuance of common stock upon exercise of stock options or awards of restricted stock units, Shares					90,188
Stock-based compensation expense	803								803
Repurchase of Class A common stock, Shares		0
Dividends paid	(2,104)								(2,104)
Change in fair value of marketable securities	534										534
Foreign currency translation gain (loss)	467										467
Net income (loss)	2,338									2,338
Balance, Ending at Jun. 30, 2020	$ 250,260				$ 6	$ 2	$ 1		$ 830,900	$ (581,130)	$ 481
Balance, Ending, Shares at Jun. 30, 2020		59,905,386	14,927,613	9,352,729	59,905,386	14,927,613	9,352,729