Debt Revolving Credit and Term Loan Agreements (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Nov. 20, 2012	Dec. 31, 2011	Sep. 20, 2010
Debt Instrument
Debt Instrument, Interest Rate at Period End	1.75%		1.68%
Consolidated Senior Secured Indebtedness to Consolidated EBITDA, Ratio	3.50
Consolidated Total Indebtedness to Consolidated EBITDA, Ratio	4.00
Portion of Rent Expense Under Capital Leases That is Treated as Interest Expense, Ratio	4.00
Debt Instrument, Basis Points	1.00
Revolving Credit Facility [Member]
Debt Instrument
Long-term Debt, Gross			$ 65,000,000
Line of Credit [Member]
Debt Instrument
Letters of Credit Outstanding, Amount	14,600,000		18,300,000
Medium-term Notes [Member]
Debt Instrument
Line of Credit Facility, Amount Outstanding		100,000,000		42,500,000
Debt Instrument, Periodic Payment, Principal	2,500,000
Debt Instrument, Final Periodic Payment, Principal	55,000,000
Long-term Debt, Gross	100,000,000		35,000,000
JPMorgan Chase Bank NA as Administrative Agent Bank of America NA and RBS Citizens NA as Co-Syndication Agents [Member] | Revolving Credit Facility [Member]
Debt Instrument
Line of Credit Facility, Maximum Borrowing Capacity		400,000,000
Line of Credit Increase in Maximum Borrowing Capacity Due to Accordian Feature	100,000,000
Long-term Debt, Gross	54,325,000
Line of Credit Facility, Remaining Borrowing Capacity	331,100,000
JPMorgan Chase Bank NA as Administrative Agent Bank of America NA and RBS Citizens NA as Co-Syndication Agents [Member] | Line of Credit [Member]
Debt Instrument
Letters of Credit Outstanding, Amount	14,600,000
Co-lead Arrangers Bank of America Securities LLC, JP Morgan Securities LLC, and RBS Citizens N.A. and a Syndicate of Lenders [Member] | Revolving Credit Facility [Member]
Debt Instrument
Line of Credit Facility, Maximum Borrowing Capacity				275,000,000
Line of Credit Facility, Amount Outstanding			65,000,000
Line of Credit Facility, Remaining Borrowing Capacity			191,700,000
Co-lead Arrangers Bank of America Securities LLC, JP Morgan Securities LLC, and RBS Citizens N.A. and a Syndicate of Lenders [Member] | Line of Credit [Member]
Debt Instrument
Letters of Credit Outstanding, Amount			18,300,000
Collateral Member One [Member] | Line of Credit [Member]
Debt Instrument
Equity Interest In Certain Foreign Subsidiaries	66.00%
Collateral Member Two [Member] | Line of Credit [Member]
Debt Instrument
Equity Interest In Domestic Subsidiaries	100.00%
Commonwealth of Australia [Member] | JPMorgan Chase Bank NA as Administrative Agent Bank of America NA and RBS Citizens NA as Co-Syndication Agents [Member] | Line of Credit [Member]
Debt Instrument
Letters of Credit Outstanding, Amount	6,700,000
Commonwealth of Australia [Member] | Co-lead Arrangers Bank of America Securities LLC, JP Morgan Securities LLC, and RBS Citizens N.A. and a Syndicate of Lenders [Member] | Line of Credit [Member]
Debt Instrument
Letters of Credit Outstanding, Amount			$ 13,100,000
Minimum [Member] | Revolving Credit Facility [Member]
Debt Instrument
Line of Credit Facility, Commitment Fee Percentage	0.20%
Minimum [Member] | Line of Credit [Member]
Debt Instrument
Line of Credit Facility, Commitment Fee Percentage	0.20%
Maximum [Member] | Revolving Credit Facility [Member]
Debt Instrument
Line of Credit Facility, Commitment Fee Percentage	0.325%
Maximum [Member] | Line of Credit [Member]
Debt Instrument
Line of Credit Facility, Commitment Fee Percentage	0.325%