Long-Term Debt (Details)	3 Months Ended	9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended						1 Months Ended	9 Months Ended
	Sep. 30, 2012 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2012 Credit agreement USD ($)	Sep. 30, 2012 Revolving credit facility due July 2016 USD ($)	Sep. 30, 2012 Revolving credit facility due November 2014 USD ($)	Sep. 30, 2012 Unsecured term loan due in February 2016	Aug. 31, 2012 Unsecured term loan due in February 2016 USD ($)	Sep. 30, 2012 Unsecured term loans guaranteed by an export credit agency Minimum	Sep. 30, 2012 Unsecured term loans guaranteed by an export credit agency Maximum	Sep. 30, 2012 Unsecured term loans guaranteed by an export credit agency Up-front Payment Arrangement Minimum	Sep. 30, 2012 Unsecured term loans guaranteed by an export credit agency Up-front Payment Arrangement Maximum	Sep. 30, 2012 Unsecured Euro-denominated term loan facility USD ($)	Jul. 31, 2012 Unsecured Euro-denominated term loan facility EUR (€)	Sep. 30, 2012 Fixed rate of 5.625% unsecured senior notes Cross currency swaps USD ($)	Sep. 30, 2012 Fixed rate of 5.625% unsecured senior notes Cross currency swaps USD ($)	Sep. 30, 2012 Fixed rate of 5.625% unsecured senior notes Cross currency swaps EUR (€)	Dec. 31, 2011 Fixed rate of 5.625% unsecured senior notes Cross currency swaps
Long-Term Debt
Interest rate on debt instrument (as a percent)														5.625%	5.625%		5.625%
Maximum borrowing capacity under credit agreement												$ 469,600,000	€ 365,000,000
Borrowing capacity			1,600,000,000	1,100,000,000	525,000,000
Floating rate base						LIBOR						EURIBOR
Margin on floating rate base (as a percent)						2.50%						3.00%
Commitment fee on undrawn amount (as a percent)												1.05%
Prepayment of unsecured floating rate term loan												100,000,000
Increase in capacity				233,000,000
Maximum cash purchase through extended tender offer														328,000,000	328,000,000	255,000,000
Premium, fees and related cost of repurchase of unsecured debt		344,150,000												344,200,000
Loss on early extinguishment of debt	7,485,000	7,485,000													7,500,000
Borrowed amount under previously committed unsecured term loan							$ 290,000,000									€ 1,000,000,000
Credit agency fees, percentage of outstanding loan balance								0.88%	1.48%
Credit agency fees, percentage of maximum loan amount payable										2.30%	2.37%