Long-Term Debt and Credit Arrangements (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Total debt	$ 290,130,000	$ 250,586,000
Less: current maturities	19,060,000	32,173,000
Total long-term debt (noncurrent)	271,070,000	218,413,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Long-term Debt, Maturities, Repayments of Principal in 2012	19,100,000
Long-term Debt, Maturities, Repayments of Principal in 2013	900,000
Long-term Debt, Maturities, Repayments of Principal in 2014	40,000,000
Long-term Debt, Maturities, Repayments of Principal in 2015	110,000,000
Long-term Debt, Maturities, Repayments of Principal in 2016	40,000,000
Long-term Debt, Maturities, Repayments of Principal thereafter	80,100,000
Letters of Credit Outstanding, Amount	10,900,000
Consolidated Fixed Charge Coverage Ratio, Minimum, Collateral Release Period	1.25
Covenant Compliance	We were in compliance with the covenants contained in our senior note agreements and Credit Agreement.
Institutional Groups One and Two [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Consolidated Leverage Ratio, Covenant	3.50
Consolidated Leverage Ratio, Maximum, Quarter Ending December 31, 2013	3.25
Consolidated Leverage Ratio, Maximum, Collateral Release Period	2.50
Senior notes payable [Member]
Debt Instrument [Line Items]
Total debt	208,333,000	216,666,000
Proceeds from Lines of Credit	70,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Line of Credit Facility, Amount Outstanding	70,000,000	0
Senior notes payable [Member] | Institutional Group One [Member]
Debt Instrument [Line Items]
Total debt	8,300,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	6.96%
Senior notes payable [Member] | Institutional Group Two [Member]
Debt Instrument [Line Items]
Total debt	200,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	6.11%
Mortgages payable [Member]
Debt Instrument [Line Items]
Total debt	11,629,000	32,670,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	4.50%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum	5.75%
Debt Instrument, Carrying Amount of Real Estate Pledged As Collateral	47,600,000
Mortgages payable [Member] | Real Estate Entities [Member]
Debt Instrument [Line Items]
Total debt	11,600,000
Less: current maturities	10,700,000
Total long-term debt (noncurrent)	900,000
Other notes payables [Member]
Debt Instrument [Line Items]
Total debt	168,000	1,250,000
Line of Credit [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	215,000,000
Debt Instrument, Basis Spread on Variable Rate	2.25%
Debt Instrument, Basis Spread on Variable Rate, LIBOR Loans	1.25%
Consolidated Tangible Net Worth, Actual	753,100,000
Consolidated Tangible Net Worth, Covenant	665,700,000
Consolidated Interest Coverage Ratio, Actual	9.52
Consolidated Interest Coverage Ratio, Covenant	4.00
Consolidated Leverage Ratio, Maximum, Collateral Release Period	2.50
Adjusted Consolidated Leverage Ratio, Actual	2.39
Line of Credit [Member] | As Of The Reporting Date [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Adjusted Consolidated Leverage Ratio, Covenant	3.25
Line of Credit [Member] | Minimum [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Line of Credit Facility, Interest Rate at Period End	2.56%
Line of Credit [Member] | Maximum [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Line of Credit Facility, Interest Rate at Period End	4.50%
Letter of Credit [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	$ 100,000,000