Debt Credit Facility Interest Rates (Details)	6 Months Ended
	Jun. 30, 2013
Unused Letters of Credit
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	1.75%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum	2.75%
Unused Revolver
Line of Credit Facility [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	0.35%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum	0.375%
Minimum
Line of Credit Facility [Line Items]
Debt Instrument Interest Rate in Addition to Libor	1.75%
Debt Instrument Interest Rate in Addition to Base Rate Borrowings	0.75%
Maximum
Line of Credit Facility [Line Items]
Debt Instrument Interest Rate in Addition to Libor	2.75%
Debt Instrument Interest Rate in Addition to Base Rate Borrowings	1.75%