Long-Term Debt and Borrowing Agreements (Details) (USD $)	9 Months Ended			9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2011 Maximum [Member]	Sep. 30, 2012 Minimum [Member]	Nov. 07, 2012 Revolving Credit Facility [Member]	Sep. 30, 2010 Revolving Credit Facility [Member]	Sep. 30, 2012 Letter of Credit [Member]	Dec. 31, 2011 Letter of Credit [Member]	Sep. 30, 2010 Letter of Credit [Member]	Sep. 30, 2010 Line of Credit [Member]
Line of Credit Facility [Line Items]
Agreement commitment						$ 50,000,000	$ 125,000,000
Accordion option							50,000,000
Swing line facility											5,000,000
Sub-facility for the issuance of LOCs										20,000,000
Outstanding Letters of Credit								5,900,000	8,400,000
Commitment fees on the unused portion of the commitment				0.35%	0.20%
Long-Term Debt and Borrowing Arrangements (Textual) [Abstract]
Borrowing outstanding under credit agreement	0		0
Borrowings under credit agreement	$ 0	$ 0