Long-Term Debt (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended					12 Months Ended		1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Jan. 31, 2012	Apr. 29, 2010	Dec. 31, 2012 Tranche 1 [Member]	Dec. 31, 2012 Tranche 2 [Member]	Dec. 31, 2011 Tranche 2 [Member]	Jan. 31, 2012 Minimum [Member]	Jan. 31, 2012 Maximum [Member]	Dec. 31, 2012 Short-term Debt [Member]
Debt Instrument [Line Items]
Line of credit facility basis spread on variable rate (in hundredths)								1.00%	1.75%
Debt instrument basis spread on variable rate (in hundredths)						0.55%
Debt instrument interest rate effective percentage (in hundredths)					5.78%	5.60%	5.60%
Repayments of notes payable						$ 30
Revolving line of facility credit maturing										8.5
Credit facility maximum borrowing capacity			400							15
Short term debt weighted average interest rate (in hundredths)										2.00%
Debt bearing fixed interest rate (in hundredths)	65.00%
Average fixed interest rate (in hundredths)	5.12%
Debt instrument face amount				50	45
Interest swap rate outstanding	33	33				30	30
Long Term Debt (Textual) [Abstract]
Interest rate on revolving credit facility (in hundredths)	3.30%	3.30%		5.46%
Average interest rate on revolving credit facility (in hundredths)	2.95%
Senior notes face amount	75
Senior notes maturities repayment date	Apr. 02, 2017
Line of credit facility variable rate basis	LIBOR
Short-term credit facility maturity date	Nov. 15, 2013
Letters of credit outstanding amount	4.2	3.7
Line of credit facility current borrowing capacity			300
Credit facility remaining borrowing capacity	$ 185.4