Employee Benefit and Incentive Plans (Details)			6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 1997 Director Plan Restricted Class A Common Stock	Jun. 30, 2012 2007 Plan Restricted Class A Common Stock		Jun. 30, 2012 2011 Plan Restricted Class A Common Stock	Jun. 30, 2012 Restricted Class A Common Stock Plans		Jun. 30, 2011 Restricted Class A Common Stock Plans	Jun. 30, 2012 1997 Director Plan Stock Units	Jun. 30, 2012 2007 Plan Stock Units	Jun. 30, 2012 2011 Plan Stock Units	Jun. 30, 2012 Stock Units Plans	Jun. 30, 2012 1997 Director Plan	Jun. 30, 2012 2007 Plan	Jun. 30, 2012 2011 Plan
Beginning balance	1,194,655			244,424			244,424		32,785	68,544	438,260	55,531	562,335	68,554	1,034,796	91,315
Granted				375,000			375,000		300,000
Granted and deferred											60,000	35,784	95,784
Vested, deferred or forfeited				(82,888)			(82,888)
Unvested share-based compensation, shares	1,194,655			536,536	[1]		536,536	[1]	244,424	68,544	498,260	91,315	658,119	68,554	1,034,796	91,315

[1] Includes (i) 275,000 performance based awards that contingently vest upon the attainment of certain specified performance measures, and (ii) 250,000 time based awards that vest based upon an employee's continued employment on pre-established vesting dates.