Treasury Stock (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Treasury Stock, Cost [Roll Forward]
Shares purchased for minimum tax withholding, cost	$ 177,000	$ 0
Common Stock Class A
Equity, Class of Stock [Line Items]
Common stock repurchase program, maximum authorized amount	35,000,000.0
Treasury Stock, Shares [Roll Forward]
Treasury stock, shares, beginning of period	11,292,220
Shares purchased for minimum tax withholding, shares	65,998
Purchase of treasury stock, shares	89,298
Treasury stock, shares, end of period	11,447,516
Treasury Stock, Cost [Roll Forward]
Treasury stock, cost, beginning of period	31,728,000
Shares purchased for minimum tax withholding, cost	177,000
Purchase of treasury stock, cost	235,000
Treasury stock, cost, end of period	$ 32,140,000
Treasury Stock, Average Cost Per Share [Roll Forward]
Treasury stock, average cost per share, beginning of period, in dollars per share	$ 2.81
Shares purchased for minimum tax withholding, average cost per share, in dollars per share	$ 2.68
Treasury stock acquired, average cost per share, in dollars per share	$ 2.63
Treasury stock, average cost per share, end of period, in dollars per share	$ 2.81