Balance Sheet Parenthetical (Parentheticals) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Class A common shares [Member]
Equity, Class of Treasury Stock [Line Items]
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	180,000,000	180,000,000
Common Stock, Shares, Issued	53,212,117	52,717,553
Common Stock, Shares, Outstanding	40,723,031	40,257,656
Treasury Stock, Shares	12,489,086	12,459,897
Class B common shares [Member]
Equity, Class of Treasury Stock [Line Items]
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	30,000,000	30,000,000
Common Stock, Shares, Issued	2,112,048	2,192,473
Common Stock, Shares, Outstanding	2,112,048	2,192,473