Long-Term Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		3 Months Ended				3 Months Ended									3 Months Ended				3 Months Ended
	Mar. 31, 2012	Mar. 31, 2013 Multi-Currency Line Of Credit [Member]	Mar. 31, 2013 Domestic And Multi-Currency Line Of Credit Up To $100,000 Due 2013 [Member]	Mar. 31, 2013 Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Dec. 31, 2012 Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2012 Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2013 Variable Rate Senior Unsecured Note Due 2015 [Member]	Dec. 31, 2012 Variable Rate Senior Unsecured Note Due 2015 [Member]	Mar. 31, 2012 Variable Rate Senior Unsecured Note Due 2015 [Member]	Mar. 31, 2013 Credit Agreement [Member]	Mar. 31, 2013 5.25% Convertible Senior Unsecured Notes Due 2029 [Member]	Mar. 31, 2013 Letter Of Credit Facility [Member]	Mar. 31, 2013 Standby Letters Of Credit [Member]	Mar. 31, 2013 LIBOR [Member] Variable Rate Senior Unsecured Note Due 2015 [Member]	Mar. 31, 2013 Agent's Base Rate [Member] Variable Rate Senior Unsecured Note Due 2015 [Member]	Mar. 31, 2013 Maximum [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member] D	Mar. 31, 2012 Maximum [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member] D	Mar. 31, 2013 Maximum [Member] LIBOR [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2013 Maximum [Member] Agent's Base Rate [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2013 Minimum [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member] D	Mar. 31, 2012 Minimum [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member] D	Mar. 31, 2013 Minimum [Member] LIBOR [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2015 [Member]	Mar. 31, 2013 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		$ 50.0	$ 100.0	$ 280.0						$ 380.0
Debt instrument, maturity year							2015				2029
Debt Instrument, Face Amount							50.0
Debt instrument basis spread on variable rate														3.50%	2.00%			3.25%	1.75%			2.00%	0.50%
Weighted average interest rate				3.04%	3.06%	3.03%	3.75%	3.75%	3.75%
Commitment fee, percentage				0.38%												0.50%				0.25%
Debt Instrument, Periodic Payment, Principal							2.1
NumberOfPricingTranches	4			3
Letter of credit facility, amount												$ 20.0	$ 16.3
Debt instrument, maturity date			May 29, 2013				Mar. 31, 2015
Debt instrument, maturity days																30	31			2	3
Debt Instrument, Date of First Required Payment							Mar. 31, 2012
Debt Instrument Frequency Of Periodic Payment							Quarterly