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Stockholders' Equity (Narrative) (Details) (USD $)
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12 Months Ended | 3 Months Ended | 12 Months Ended | 4 Months Ended | 12 Months Ended | 0 Months Ended | 12 Months Ended | 0 Months Ended | 12 Months Ended | ||||||||||||||
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Dec. 31, 2011
years
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Dec. 31, 2010
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Dec. 31, 2009
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Mar. 31, 2011
1999 Stock Option Plan And 2007 Equity Incentive Plan [Member]
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Dec. 31, 2011
1999 Stock Option Plan And 2007 Equity Incentive Plan [Member]
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Dec. 31, 2010
1999 Stock Option Plan And 2007 Equity Incentive Plan [Member]
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Dec. 31, 2011
2007 Equity Incentive Plan [Member]
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Dec. 31, 2011
Restricted Stock [Member]
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Dec. 31, 2010
Restricted Stock [Member]
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Dec. 31, 2009
Restricted Stock [Member]
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May 04, 2010
Stock Options [Member]
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Dec. 31, 2011
Stock Options [Member]
years
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Dec. 31, 2011
Restricted Stock And Restricted Stock Units [Member]
years
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Dec. 31, 2011
Restricted Stock Units (RSUs) [Member]
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Dec. 31, 2010
Restricted Stock Units (RSUs) [Member]
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Dec. 31, 2009
Restricted Stock Units (RSUs) [Member]
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Jul. 02, 2010
Nexius, Inc. [Member]
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Dec. 31, 2011
Nexius, Inc. [Member]
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Aug. 31, 2010
Nedstat B.V. [Member]
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Dec. 31, 2011
Nedstat B.V. [Member]
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Dec. 31, 2011
AdXpose [Member]
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Dec. 31, 2011
Minimum [Member]
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Dec. 31, 2011
Maximum [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||||||||||||||||||||||
| Number of shares authorized | 1,800,000 | 7,200,000 | 5,900,000 | ||||||||||||||||||||
| Percentage common stock outstanding shares | 4.00% | ||||||||||||||||||||||
| Description of shares available for future issuance | In addition, the 2007 Plan provides for annual increases in the number of shares available for issuance thereunder on the first day of each fiscal year beginning with the 2008 fiscal year, equal to the lesser of: (i) 4% of the outstanding shares of the Company's common stock on the last day of the immediately preceding fiscal year; (ii) 1,800,000 shares; or (iii) such other amount as the Company's board of directors may determine. | ||||||||||||||||||||||
| Increase in number of shares available for grant | 1,260,942 | ||||||||||||||||||||||
| Vesting period of options granted | four | ||||||||||||||||||||||
| Options expiration period | 10 | ||||||||||||||||||||||
| Shares available for grant | 2,121,449 | ||||||||||||||||||||||
| Description of vesting percentage | These awards are subject to market-based vesting, whereby 100% of the shares subject to the awards will vest in the event that the Company's common stock closing price exceeds an average of $30 per share for a consecutive thirty-day period prior to May 4, 2012 (the "Trigger"). 50% of the shares subject to the awards will vest upon achievement of the Trigger and the remaining 50% of the shares subject to the awards will vest on the one year anniversary of the achievement of the Trigger, subject to the employee's continued status as a service provider of the Company through such dates. | ||||||||||||||||||||||
| Percentage of common shares subject to option | 100.00% | ||||||||||||||||||||||
| Common ctock closing price threshold for full award vesting | $ 30.00 | ||||||||||||||||||||||
| Award vesting percentage subject to achievement of Trigger | 50.00% | ||||||||||||||||||||||
| Award vesting percentage subject to achievement of Trigger at anniversary | 50.00% | ||||||||||||||||||||||
| Stock-based compensation expense | $ 3,100,000 | $ 3,800,000 | |||||||||||||||||||||
| Weighted average grant date fair value of options granted | $ 18.21 | ||||||||||||||||||||||
| Total fair value of shares vested | 100,000 | 100,000 | 500,000 | ||||||||||||||||||||
| Aggregate intrinsic value of options exercised | 3,600,000 | 4,700,000 | 4,300,000 | ||||||||||||||||||||
| Aggregate intrinsic value of options outstanding | 12,300,000 | ||||||||||||||||||||||
| Aggregate intrinsic value of options exercisable | 9,200,000 | ||||||||||||||||||||||
| Weighted-average remaining contractual term for options outstanding (in years) | 3.07 | ||||||||||||||||||||||
| Weighted-average remaining contractual term for options exercisable (in years) | 2.45 | ||||||||||||||||||||||
| Total unrecognized compensation expense | 300,000 | 20,700,000 | |||||||||||||||||||||
| Weighted average period expected to recognize compensation expense (in years) | 0.16 | 1.52 | |||||||||||||||||||||
| Right of repurchase of shares awarded, lapse rate | 25.00% | ||||||||||||||||||||||
| Aggregate intrinsic value for non-vested shares | 38,500,000 | ||||||||||||||||||||||
| Weighted average remaining contractual term for non-vested shares (in years) | 2.02 | ||||||||||||||||||||||
| Restricted stock forfeited, shares | 35,831 | ||||||||||||||||||||||
| Restricted stock units vested, shares | 868,736 | 945,523 | 421,102 | 751,873 | 856,964 | 393,764 | 868,736 | 116,863 | 88,559 | 27,338 | |||||||||||||
| Number of shares repurchased | 289,637 | ||||||||||||||||||||||
| Aggregate purchase price of share repurchased | $ 7,400,000 | ||||||||||||||||||||||
| Warrants granted to purchase common stock | 403,368 | ||||||||||||||||||||||
| Warrants to purchase common stock | 24,375 | 24,375 | |||||||||||||||||||||
| Common stock warrants expiration date, range, start | February 2006 | ||||||||||||||||||||||
| Common stock warrants expiration date, range, end | April 2015 | ||||||||||||||||||||||
| Common stock warrants exercise price | 3.00 | 24.50 | |||||||||||||||||||||
| Number of shares issued as consideration | 974,358 | 158,070 | 158,070 | 58,045 | 58,045 | 982,285 | |||||||||||||||||
| Percentage of shares issued pursuant to term of stock purchase agreement | 30.00% | ||||||||||||||||||||||