Long-Term Obligations (Schedule Of Long-Term Obligations) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Eurodollar loans under five-year revolving credit agreement bearing annual interest equal to the British Bankers Association LIBOR Rate ("BBA LIBOR") plus an applicable margin based on the Company's consolidated leverage ratio (consolidated funded indebtedness to consolidated EBITDA)	$ 170,000,000	$ 100,000,000
Other long-term obligations	1,736,000	1,710,000
Contingent consideration	21,595,000	21,595,000
Unsecured acquisition obligations, net of imputed interest, payable in various installments through 2015	18,855,000	20,996,000
Total long-term obligations	726,974,000	653,910,000
Less: current installments	463,536,000	397,132,000
Long-term obligations, excluding current installments	263,438,000	256,778,000
Convertible debt, fixed interest rate	2.75%
Option 2012 [Member]
Debt Instrument [Line Items]
Principal amount of convertible debentures	275,000,000	275,000,000
Unamortized discount	(6,395,000)	(9,059,000)
Convertible debt, fixed interest rate	2.75%	2.75%
Convertible debt, maturity date	2037
Option 2014 [Member]
Debt Instrument [Line Items]
Principal amount of convertible debentures	275,000,000	275,000,000
Unamortized discount	$ (28,817,000)	$ (31,332,000)
Convertible debt, fixed interest rate	2.75%	2.75%
Convertible debt, maturity date	2037