Long Term Debt (Details Textuals 1) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Pre May Amendment [Member]
Line of Credit Facility [Line Items]
Leverage Ratios	5.0 to 1.0
Post May Amendment [Member]
Line of Credit Facility [Line Items]
Leverage Ratios	5.5 to 1.0
During Acquisition [Member]
Line of Credit Facility [Line Items]
Leverage Ratios	5.5 to 1.0
2016 Letter of Credit [Member]
Line of Credit Facility [Line Items]
Borrowed under existing credit facility	48.0
Outstanding letter of credit	57.6
Avaliable Borrowing Capacity	529.4
2016 Letter of Credit [Member] | Line Of Credit Amendment Date 1 [Member]
Line of Credit Facility [Line Items]
Line of credit facility, amended date	January, 2012
2016 Letter of Credit [Member] | Line Of Credit Amendment Date 2 [Member]
Line of Credit Facility [Line Items]
Line of credit facility, amended date	May 2012
2016 Letter of Credit [Member] | Preamendment Credit Facility [Member]
Line of Credit Facility [Line Items]
Preamendment borrowing capacity	485.0
2016 Letter of Credit [Member] | Postamendment Credit Facility [Member]
Line of Credit Facility [Line Items]
Postamendment borrowing capacity	635.0