Condensed Consolidated Balance Sheets Parenthetical (USD $) In Thousands, except Per Share data	Jun. 30, 2011	Dec. 31, 2010
Current assets
Allowance for doubtful accounts	$ 1,750	$ 1,347
Other assets
Accumulated depreciation on property and equipment	29,511	26,375
Accumulated amortization on intangible assets	$ 22,705	$ 20,656
Stockholders' equity
Preferred stock, shares authorized	50,000	50,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common Stock Class A
Stockholders' equity
Common Stock, Par Value	$ 0.01	$ 0.01
Common Stock, shares authorized	100,000	100,000
Common Stock, shares issued	31,648	30,166
Common Stock, shares outstanding	31,648	30,166
Common Stock Class B
Stockholders' equity
Common Stock, Par Value	$ 0.0001	$ 0.0001
Common Stock, shares authorized	50,000	50,000
Common Stock, shares issued	10,818	11,151
Common Stock, shares outstanding	10,818	11,151