Long-Term Obligations (Schedule Of Long-Term Debt) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Promissory notes	$ 7,900,000	$ 14,400,000
Long-term debt including current portion	145,400,000	181,900,000
Current portion of long-term obligations	(33,900,000)	(37,200,000)
Total	111,500,000	144,700,000
Series A Notes [Member]
Debt Instrument [Line Items]
Principal amount	35,000,000
Senior long-term notes, interest rate	6.07%
Maturity date	Mar. 25, 2013
Senior Notes	35,000,000	35,000,000
Series B Notes [Member]
Debt Instrument [Line Items]
Principal amount	30,000,000
Senior long-term notes, interest rate	6.28%
Maturity date	Mar. 25, 2014
Senior Notes	30,000,000	30,000,000
Series C Notes [Member]
Debt Instrument [Line Items]
Principal amount	35,000,000
Senior long-term notes, interest rate	6.49%
Maturity date	Mar. 25, 2015
Senior Notes	35,000,000	35,000,000
Term Loan [Member]
Debt Instrument [Line Items]
Principal amount	150,000,000
Term loan principal payments plus accrued interest payable, quarterly	7,500,000
Eurodollar Rate plus the applicable percentage	1.05%
Maturity date	Mar. 26, 2013
Senior Notes	$ 37,500,000	$ 67,500,000