Long-Term Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Domestic And Multi Currency Line Of Credit Up To $380 Due 2015 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 380.0
Multi Currency Line Of Credit Fifty Million Due 2015[Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	0
Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	280.0
Weighted average interest rate		2.77%	3.06%
Commitment fee, percentage	0.38%
NumberOfPricingTranches		3
Debt Issuance Costs	1.8
Debt Instrument, Decrease, Repayments	202.0
Domestic And Multi-Currency Line Of Credit Up To $100,000 Due 2018 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	100.0
Variable Rate Senior Unsecured Note Due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity year	2018
Debt Instrument, Face Amount	50.0
Weighted average interest rate	3.75%	3.75%	3.75%
Debt Instrument, Periodic Payment, Principal	2.1
Debt instrument, maturity date	Mar. 31, 2018
Debt Instrument Frequency Of Periodic Payment	Quarterly
5.75% $300 Million Senior Unsecured Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount	300.0
Issurance Cost Amortization Period, in years	5
Debt Issuance Costs	8.1
Debt instrument, interest rate	5.75%
Debt instrument, maturity date	May 15, 2018
Debt Instrument, Issuance Date	May 15, 2013
Letter Of Credit Facility [Member]
Debt Instrument [Line Items]
Letter of credit facility, amount	20.0
Standby Letters Of Credit [Member]
Debt Instrument [Line Items]
Letter of credit facility, amount	$ 16.3
LIBOR [Member] | Variable Rate Senior Unsecured Note Due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate	3.50%
Agent's Base Rate [Member] | Variable Rate Senior Unsecured Note Due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate	2.00%
Maximum [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]
Debt Instrument [Line Items]
Commitment fee, percentage	0.50%
Debt instrument, maturity days		6
Maximum [Member] | LIBOR [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate	3.25%
Maximum [Member] | Agent's Base Rate [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate	1.75%
Minimum [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]
Debt Instrument [Line Items]
Commitment fee, percentage	0.25%
Debt instrument, maturity days		1
Minimum [Member] | LIBOR [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate	2.00%
Minimum [Member] | Agent's Base Rate [Member] | Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]
Debt Instrument [Line Items]
Debt instrument basis spread on variable rate	0.50%