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, 2012	$ 5,401				$ 5	$ 2	$ 1		$ 930,814	$ (925,421)
Balance, Beginning, Shares at Dec. 31, 2012					54,404,226	22,188,161	9,352,729
Issuance of common stock upon exercise of stock options or awards of restricted stock units	$ 2,807				$ 1				2,806
Issuance of common stock upon exercise of stock options or awards of restricted stock units, Shares	1,683,000				2,170,438
Stock-based compensation expense	$ 4,771								4,771
Class B common stock exchanged for Class A common stock					3,218,939	(3,218,939)
Dividends paid	(11,014)								(11,014)
Change in fair value of interest rate swap agreements	234										$ 234
Net income	133,825									133,825
Balance, Ending at Dec. 31, 2013	136,024				$ 6	$ 2	$ 1		927,377	(791,596)	234
Balance, Ending, Shares at Dec. 31, 2013					59,793,603	18,969,222	9,352,729
Issuance of common stock upon exercise of stock options or awards of restricted stock units	$ 1,841								1,841
Issuance of common stock upon exercise of stock options or awards of restricted stock units, Shares	1,042,000				1,531,100
Stock-based compensation expense	$ 4,351								4,351
Class B common stock exchanged for Class A common stock					39,187	(39,187)
Repurchase of Class A common stock	(12,543)	$ (12,500)							(12,543)
Repurchase of Class A common stock, Shares		(2,500,000)						(2,469,920)
Retirement of treasury stock, Shares					(2,469,920)			2,469,920
Dividends paid	(8,865)								(8,865)
Change in fair value of interest rate swap agreements	(2,372)										(2,372)
Net income	27,122									27,122
Balance, Ending at Dec. 31, 2014	145,558				$ 6	$ 2	$ 1		912,161	(764,474)	(2,138)
Balance, Ending, Shares at Dec. 31, 2014		58,893,970	18,930,035	9,352,729	58,893,970	18,930,035	9,352,729
Issuance of common stock upon exercise of stock options or awards of restricted stock units	$ 2,177								2,177
Issuance of common stock upon exercise of stock options or awards of restricted stock units, Shares	966,000				1,580,779
Stock-based compensation expense	$ 5,240								5,240
Class B common stock exchanged for Class A common stock					4,002,422	(4,002,422)
Repurchase of Class A common stock, Shares		0
Dividends paid	(9,350)								(9,350)
Change in fair value of interest rate swap agreements	(1,977)										(1,977)
Net income	25,625									25,625
Balance, Ending at Dec. 31, 2015	$ 167,273				$ 6	$ 2	$ 1		$ 910,228	$ (738,849)	$ (4,115)
Balance, Ending, Shares at Dec. 31, 2015		64,477,171	14,927,613	9,352,729	64,477,171	14,927,613	9,352,729