Consolidated Statement Of Stockholders' Equity (Unaudited) - 9 months ended Sep. 30, 2016 - USD ($) $ in Thousands	Total	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]	Noncontrolling Interest [Member]	Class A Common Stock [Member]	Class B Common Stock [Member]
Beginning balance, shares at Dec. 31, 2015						87,808,801	50,991,938
Beginning balance, value at Dec. 31, 2015	$ 617,127	$ 754,589	$ (139,033)	$ 81	$ 102	$ 878	$ 510
Common stock issued under stock plans, shares						785,416
Common stock issued under stock plans, value	5,175	5,167				$ 8
Stock-based compensation expense	4,691	4,691
Excess tax benefit from stock-based compensation	547	547
Shares issued under employee stock purchase plan, shares						63,941
Shares issued under employee stock purchase plan, value	$ 955	955				$ 0
Repurchase and cancellation of Class A Common Stock, shares	(7,293,000)					(7,292,910)
Repurchase and cancellation of Class A Common Stock, value	$ (115,000)	(75,632)	(39,295)			$ (73)
Conversion of Class B common stock to Class A common stock, shares						1,250,000	(1,250,000)
Conversion of Class B common stock to Class A common stock, value	0					$ 13	$ (13)
Net income	98,825		98,825
Other comprehensive income (loss), net of income taxes	(81)			(81)
Ending balance, shares at Sep. 30, 2016						82,615,248	49,741,938
Ending balance, value at Sep. 30, 2016	$ 612,239	$ 690,317	$ (79,503)	$ 0	$ 102	$ 826	$ 497