Prior Revolving Credit Facility Lines of Credit Narrative (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Nov. 07, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 75,000,000	$ 175,000,000
Swing line sub-limit		7,000,000
Letter of Credit sub-limit	35,000,000	50,000,000
Maximum Borrowing Capacity under Accordion Feature		225,000,000
Revolving credit facility	53,200,000		0
Letters of Credit Outstanding, Amount	11,500,000	12,000,000
Debt, Weighted Average Interest Rate	4.20%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%
Line of Credit Facility, Remaining Borrowing Capacity	$ 10,300,000	$ 73,000,000