Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2013

Stockholders' Equity Note [Abstract]

Schedule of change in the number of shares of Class A common stock

The following table sets forth the change in the number of shares of our Class A common stock outstanding during the three months ended March 31, 2013 and during the fiscal year ended December 31, 2012:

	Three Months Ended		Twelve Months Ended
	March 31, 2013		December 31, 2012
Shares outstanding as of beginning of period	84,395		92,433
Shares issued as part of equity-based compensation plans and the Employee    Stock Purchase Plan, net of restricted stock units surrendered	818		1,119
Shares repurchased into treasury stock	(226	)	(9,157	)
Shares outstanding as of end of period	84,987		84,395