Derivative Instruments and Hedging Activities (Details) In Thousands, unless otherwise specified			3 Months Ended
	Mar. 31, 2014 item	Dec. 31, 2013 item	Mar. 31, 2014 Foreign exchange contracts USD ($)	Mar. 31, 2013 Foreign exchange contracts USD ($)	Mar. 31, 2014 Forward contracts Purchases U.S. dollars: British pounds sterling USD ($)	Mar. 31, 2014 Forward contracts Purchases U.S. dollars: Australian dollars USD ($)	Mar. 31, 2014 Forward contracts Purchases Euros : U.S. dollars EUR (€)	Mar. 31, 2014 Forward contracts Sales U.S. dollars: British pounds sterling GBP (£)	Mar. 31, 2014 Forward contracts Sales U.S. dollars: Australian dollars AUD	Mar. 31, 2014 Forward contracts Sales Euros : U.S. dollars USD ($)
Derivative Instruments and Hedging Activities
Targeted percentage of debt portfolio to be fixed with interest rates	75.00%
Number of derivative instrument with contingent features of credit risk	0	0
Derivative instruments
Notional amount of derivatives					$ 302,009	$ 61,707	€ 167,000	£ 182,500	67,000	$ 229,578
Net cash receipts from foreign currency forward contracts				5,799
Net cash payments from foreign currency forward contracts			$ 7,199