Debt (Narrative) (Details) (USD $)	3 Months Ended			9 Months Ended							9 Months Ended
	Sep. 30, 2013	Feb. 08, 2013	Nov. 18, 2010	Sep. 30, 2013 7.875% Senior Unsecured Notes [Member]	Dec. 31, 2012 7.875% Senior Unsecured Notes [Member]	Feb. 01, 2012 7.875% Senior Unsecured Notes [Member]	Sep. 30, 2013 Unsecured Debt [Member]	Feb. 01, 2012 Unsecured Debt [Member]	Sep. 30, 2013 Senior Secured Credit Facility [Member]	Sep. 30, 2013 Senior Secured Credit Facility [Member] Letters Of Credit [Member]	Sep. 30, 2013 Five Point Seventy Five Percentage Senior Unsecured Notes [Member]	Sep. 30, 2013 Amended Facility [Member]	Sep. 30, 2013 Maximum [Member] Senior Secured Credit Facility [Member] Letters Of Credit [Member]	Sep. 30, 2013 Petroleum Products [Member] Senior Secured Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, amount outstanding									$ 411,300,000					$ 97,100,000
Credit facility, maximum borrowing capacity												1,000,000,000
Letters of credit, outstanding amount										15,300,000			100,000,000
Credit facility and senior unsecured notes, maturity dates	Feb. 15, 2021
Total amount available for borrowings under credit facility									573,400,000
Senior unsecured notes, principal amount		350,000,000	250,000,000			100,000,000	350,000,000
Senior unsecured notes, stated rate		5.75%	7.875%	7.875%							5.75%
Senior unsecured notes, percentage of face value								101.00%
Debt Instrument, Interest Rate, Effective Percentage								7.682%
Debt Instrument, Unamortized Premium				$ 804,000	$ 895,000
Maximum Percentage Of Principal, Early Debt Redemption				35.00%							35.00%
Redemption premium for notes				107.875%							105.75%