Capital Structure (Details) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Units Exchanged for Shares of Class A Common Stock [Line Items]
Exchange of New Class A Units to shares of Class A common stock, shares	0	0	0
Common Stock Class A [Member]
Schedule of Units Exchanged for Shares of Class A Common Stock [Line Items]
Exchange of New Class A Units to shares of Class A common stock, shares	6,081	653	1,788