Financing (Details) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2011	Oct. 01, 2011
Short-term borrowings [Abstract]
Notes payable, non-interest bearing	$ 240,000	$ 285,000
Total short-term borrowings	40,240,000	40,285,000
Line of Credit Facility [Abstract]
Maturity date of line of credit	Jan. 31, 2012
Unsecured Line of Credit Facility [Member]
Line of Credit Facility [Abstract]
Line of credit facility, amount outstanding	40,000,000	40,000,000
Line of credit facility, interest rate description	LIBOR+0.45
Line of credit facility, interest rate at period end (in hundredths)	0.76%
Line of credit facility, borrowing capacity	75,000,000	75,000,000
Line of credit facility, remaining borrowing capacity	27,200,000
Notional amounts of outstanding interest rate swaps	40,000,000	24,000,000
Weighted average fixed interest rate payable (in hundredths)	2.09%	2.47%
Basis-point differential between the variable rate interest paid on outstanding credit facility borrowings and the variable rate interest received on the interest rate swaps	45
Effective interest rate applicable to outstanding credit facility (in hundredths)	2.54%	2.92%
Letters of Credit and Guarantees [Member]
Line of Credit Facility [Abstract]
Letters of credit outstanding, amount	$ 7,800,000