Subsequent Events (Details) (USD $) In Millions, except Share data, unless otherwise specified			0 Months Ended	1 Months Ended		0 Months Ended	1 Months Ended	0 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Dec. 20, 2012 Management Units	Apr. 30, 2011 Management Units	Jun. 30, 2013 Management Units	Jul. 29, 2013 Subsequent events item	Jul. 31, 2013 Subsequent events Management Units	Jul. 29, 2013 Subsequent events Senior secured revolving credit facility	Jul. 29, 2013 Subsequent events Class A common stock	Jul. 23, 2013 Subsequent events Class A common stock
Subsequent events
Number of classes of common stock authorized for offering						2
Shares issued										12,500,000
Price per share (in dollars per share)										$ 15.00
Expenses and underwriting discounts and commissions									$ 10.5
Net proceeds received									177.0
Net proceeds received, net of estimated offering expenses									173.0
Repayment of debt								$ 167.0
Issuance of Management Units
Management units, issued	3,194,444	3,194,444	944,444	2,250,000	576,000		993,944
Vesting period of units			5 years	5 years			5 years
Unit issue price (in dollars per unit)			$ 8.71				$ 8.71