Long-Term Debt (Narrative) (Details) (USD $)			3 Months Ended												3 Months Ended				3 Months Ended
	Nov. 29, 2011 Additional Credit Facility [Member]	Mar. 31, 2012 Multi-Currency Line Of Credit [Member]	Mar. 31, 2012 Domestic And Multi-Currency Line Of Credit Up To $100,000 Due 2013 [Member]	Mar. 31, 2012 Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2011 Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2012 Variable Rate Senior Unsecured Note Due 2015 [Member]	Mar. 31, 2012 Credit Agreement [Member]	Nov. 29, 2011 Credit Agreement [Member]	Mar. 30, 2011 Credit Agreement [Member]	Mar. 31, 2012 5.25% Convertible Senior Unsecured Notes Due 2029 [Member]	Mar. 30, 2011 Letter Of Credit Facility [Member]	Mar. 31, 2012 Standby Letters Of Credit [Member]	Mar. 31, 2012 LIBOR [Member] Variable Rate Senior Unsecured Note Due 2015 [Member]	Mar. 31, 2012 Agent's Base Rate [Member] Variable Rate Senior Unsecured Note Due 2015 [Member]	Mar. 31, 2012 Maximum [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2011 Maximum [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2012 Maximum [Member] LIBOR [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2012 Maximum [Member] Agent's Base Rate [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2012 Minimum [Member]	Mar. 31, 2012 Minimum [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2011 Minimum [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2012 Minimum [Member] LIBOR [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2012 Minimum [Member] Agent's Base Rate [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 100,000,000	$ 50,000,000	$ 100,000,000	$ 280,000,000			$ 380,000,000	$ 430,000,000	$ 330,000,000
Debt instrument, maturity year			2013	2015		2015				2029
Proceeds from initial public offering																			350,000,000
Aggregate principal amount of senior notes						50,000,000
Debt instrument basis spread on variable rate													3.50%	2.00%			3.25%	1.75%				2.00%	0.50%
Commitment fee, percentage				0.38%											0.50%					0.25%
Weighted average interest rate				3.03%		3.75%
Debt payable in quarterly installments starting March 12, 2012						2,100,000
Number of pricing tranches				4	4
Letter of credit facility, amount											$ 20,000,000	$ 18,100,000
Debt instrument, maturity date			May 29, 2013			Mar. 31, 2015
Debt instrument, maturity days															31	31				3	3