CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Total	Class A and B Common Stock [Member]	Additional Paid-in Capital [Member]	Purchase Price Of Excess Of Predecessor Basis, Net Of Tax [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2014	$ 600,784	$ 419	$ 171,235	$ (15,458)	$ 589,809	$ (77)	$ (145,144)
Beginning Balance (in shares) at Dec. 31, 2014		41,887,088					(4,977,468)
Purchase of treasury shares	(28,823)						$ (28,823)
Purchase of treasury shares (in shares)							(735,524)
Stock tendered for payments of withholding taxes	(2,916)						$ (2,916)
Stock tendered for payments of withholding taxes (in shares)							(77,732)
Issuance of restricted stock awards, net of forfeitures			(4,897)				$ 4,897
Issuance of restricted stock awards, net of forfeitures (in shares)							199,893
Share-based compensation expense	7,833		7,833
Tax benefit of share-based compensation plans	114		114
Net income	70,949				70,949
Foreign currency translation adjustment	(101)					(101)
Ending Balance at Dec. 31, 2015	647,840	$ 419	174,285	(15,458)	660,758	(178)	$ (171,986)
Ending Balance (in shares) at Dec. 31, 2015		41,887,088					(5,590,831)
Purchase of treasury shares	(100,000)						$ (100,000)
Purchase of treasury shares (in shares)							(2,672,227)
Stock tendered for payments of withholding taxes	(2,489)						$ (2,489)
Stock tendered for payments of withholding taxes (in shares)							(73,546)
Issuance of restricted stock awards, net of forfeitures			(8,838)				$ 8,838
Issuance of restricted stock awards, net of forfeitures (in shares)							304,794
Share-based compensation expense	8,479		8,479
Tax benefit of share-based compensation plans	(361)		(361)
Net income	74,805				74,805
Foreign currency translation adjustment	(95)					(95)
Ending Balance at Dec. 31, 2016	628,179	$ 419	173,565	(15,458)	735,563	(273)	$ (265,637)
Ending Balance (in shares) at Dec. 31, 2016		41,887,088					(8,031,810)
Stock tendered for payments of withholding taxes	(3,412)						$ (3,412)
Stock tendered for payments of withholding taxes (in shares)							(77,988)
Issuance of restricted stock awards, net of forfeitures			(10,427)				$ 10,427
Issuance of restricted stock awards, net of forfeitures (in shares)							332,076
Share-based compensation expense	9,873		9,873
Net income	135,153				135,153
Foreign currency translation adjustment	79					79
Ending Balance at Dec. 31, 2017	$ 769,872	$ 419	$ 173,011	$ (15,458)	$ 870,716	$ (194)	$ (258,622)
Ending Balance (in shares) at Dec. 31, 2017		41,887,088					(7,777,722)