Long-Term Debt and Credit Arrangements (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Total debt	$ 250,586,000	$ 280,470,000
Less: current maturities	32,173,000	38,119,000
Total long-term debt (noncurrent)	218,413,000	242,351,000
Long-term Debt, by Maturity [Abstract]
Long-term Debt, Maturities, Repayments of Principal in 2012	32,200,000
Long-term Debt, Maturities, Repayments of Principal in 2013	18,300,000
Long-term Debt, Maturities, Repayments of Principal in 2014	0
Long-term Debt, Maturities, Repayments of Principal in 2015	40,000,000
Long-term Debt, Maturities, Repayments of Principal in 2016	40,000,000
Long-term Debt, Maturities, Repayments of Principal thereafter	120,100,000
Line of Credit Facility, Amount Outstanding	0
Letters of Credit Outstanding, Amount	4,200,000
Covenant Compliance	We were in compliance with the covenants contained in our senior note agreements and Credit Agreement.
Senior notes payable [Member]
Debt Instrument [Line Items]
Total debt	216,666,000	225,000,000
Senior notes payable [Member] | Institutional Group One [Member]
Debt Instrument [Line Items]
Total debt	16,700,000
Long-term Debt, by Maturity [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	6.96%
Consolidated Net Worth	799,200,000
Consolidated Net Worth, Covenant	686,500,000
Senior notes payable [Member] | Institutional Group Two [Member]
Debt Instrument [Line Items]
Total debt	200,000,000
Long-term Debt, by Maturity [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	6.11%
Consolidated Net Worth	799,200,000
Consolidated Net Worth, Covenant	697,400,000
Mortgages payable [Member]
Debt Instrument [Line Items]
Total debt	32,670,000	55,300,000
Long-term Debt, by Maturity [Abstract]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	3.75%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum	7.00%
Debt Instrument, Carrying Amount of Real Estate Pledged As Collateral	64,600,000
Debt Instrument, Increase, Additional Borrowings	8,400,000
Mortgages payable [Member] | Real Estate Entities [Member]
Debt Instrument [Line Items]
Total debt	32,500,000
Less: current maturities	22,600,000
Total long-term debt (noncurrent)	9,900,000
Other notes payables [Member]
Debt Instrument [Line Items]
Total debt	1,250,000	170,000
Line of Credit [Member]
Long-term Debt, by Maturity [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	100,000,000
Debt Instrument, Basis Spread on Variable Rate	2.75%
Consolidated Tangible Net Worth, Actual	757,700,000
Consolidated Tangible Net Worth, Covenant	665,800,000
Consolidated Interest Coverage Ratio, Actual	10.06
Consolidated Interest Coverage Ratio, Covenant	4.00
Adjusted Consolidated Leverage Ratio, Actual	1.42
Adjusted Consolidated Leverage Ratio, Covenant, Quarterly Decrease	0.25
Line of Credit [Member] | As Of The Reporting Date [Member]
Long-term Debt, by Maturity [Abstract]
Adjusted Consolidated Leverage Ratio, Covenant	3.75
Line of Credit [Member] | Range, As Of The Reporting Date to March 2012 [Member]
Long-term Debt, by Maturity [Abstract]
Adjusted Consolidated Leverage Ratio, Covenant	3.75
Line of Credit [Member] | After 2013 [Member]
Long-term Debt, by Maturity [Abstract]
Adjusted Consolidated Leverage Ratio, Covenant	3.00
Line of Credit [Member] | Minimum [Member]
Long-term Debt, by Maturity [Abstract]
Line of Credit Facility, Interest Rate at Period End	3.05%
Line of Credit [Member] | Maximum [Member]
Long-term Debt, by Maturity [Abstract]
Line of Credit Facility, Interest Rate at Period End	3.88%
Letter of Credit [Member]
Long-term Debt, by Maturity [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	$ 50,000,000