UNAUDITED CONSOLIDATED STATEMENTS STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Cumulative Effect Period Of Adoption Adjustment [Member]	Class A and B Common Stock [Member]	Additional Paid-in Capital [Member]	Purchase Price in Excess of Predecessor Basis, Net of Tax [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect Period Of Adoption Adjustment [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2018	$ 980,834	$ (26)	$ 419	$ 172,220	$ (15,458)	$ 1,072,456	$ (26)	$ (182)	$ (248,621)
Beginning Balance (in shares) at Dec. 31, 2018			41,887,088						(7,431,083)
Purchase of treasury stock	(7,282)								$ (7,282)
Purchase of treasury stock (in shares)									(181,811)
Stock withheld for payments of withholding taxes	(2,746)								$ (2,746)
Stock withheld for payments of withholding taxes (in shares)									(72,713)
Issuance of restricted stock awards, net of forfeitures				(10,288)					$ 10,288
Issuance of restricted stock awards, net of forfeitures (in shares)									316,555
Share-based compensation expense	8,687			8,687
Net income	$ 53,111					53,111
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Foreign currency translation adjustment	$ 4							4
Ending Balance at Jun. 30, 2019	1,032,582		$ 419	170,619	(15,458)	1,125,541		(178)	$ (248,361)
Ending Balance (in shares) at Jun. 30, 2019			41,887,088						(7,369,052)
Beginning Balance at Mar. 31, 2019	1,007,064		$ 419	163,340	(15,458)	1,096,324		(175)	$ (237,386)
Beginning Balance (in shares) at Mar. 31, 2019			41,887,088						(7,114,310)
Purchase of treasury stock	(7,282)								$ (7,282)
Purchase of treasury stock (in shares)									(181,811)
Stock withheld for payments of withholding taxes	(168)								$ (168)
Stock withheld for payments of withholding taxes (in shares)									(3,805)
Issuance of restricted stock awards, net of forfeitures				3,525					$ (3,525)
Issuance of restricted stock awards, net of forfeitures (in shares)									(69,126)
Share-based compensation expense	3,754			3,754
Net income	29,217					29,217
Foreign currency translation adjustment	(3)							(3)
Ending Balance at Jun. 30, 2019	1,032,582		$ 419	170,619	(15,458)	1,125,541		(178)	$ (248,361)
Ending Balance (in shares) at Jun. 30, 2019			41,887,088						(7,369,052)
Beginning Balance at Dec. 31, 2019	1,075,279		$ 419	179,637	(15,458)	1,179,601		(186)	$ (268,734)
Beginning Balance (in shares) at Dec. 31, 2019			41,887,088						(7,870,888)
Stock withheld for payments of withholding taxes	(3,944)								$ (3,944)
Stock withheld for payments of withholding taxes (in shares)									(75,595)
Issuance of restricted stock awards, net of forfeitures				(8,932)					$ 8,932
Issuance of restricted stock awards, net of forfeitures (in shares)									239,845
Share-based compensation expense	8,209			8,209
Net income	26,390					26,390
Foreign currency translation adjustment	(97)							(97)
Ending Balance at Jun. 30, 2020	1,105,837		$ 419	178,914	(15,458)	1,205,991		(283)	$ (263,746)
Ending Balance (in shares) at Jun. 30, 2020			41,887,088						(7,706,638)
Beginning Balance at Mar. 31, 2020	1,088,709		$ 419	175,370	(15,458)	1,192,837		(320)	$ (264,139)
Beginning Balance (in shares) at Mar. 31, 2020			41,887,088						(7,680,505)
Stock withheld for payments of withholding taxes	(175)								$ (175)
Stock withheld for payments of withholding taxes (in shares)									(3,878)
Issuance of restricted stock awards, net of forfeitures				(568)					$ 568
Issuance of restricted stock awards, net of forfeitures (in shares)									(22,255)
Share-based compensation expense	4,112			4,112
Net income	13,154					13,154
Foreign currency translation adjustment	37							37
Ending Balance at Jun. 30, 2020	$ 1,105,837		$ 419	$ 178,914	$ (15,458)	$ 1,205,991		$ (283)	$ (263,746)
Ending Balance (in shares) at Jun. 30, 2020			41,887,088						(7,706,638)