Long-term Debt Outstanding Revolving Loans (Details) € in Thousands, £ in Thousands, CAD in Thousands, AUD in Thousands, $ in Thousands	Dec. 31, 2015 AUD	Dec. 31, 2015 GBP (£)	Dec. 31, 2015 EUR (€)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 CAD	Dec. 31, 2014 AUD	Dec. 31, 2014 EUR (€)	Dec. 31, 2014 USD ($)	Dec. 31, 2014 CAD
Line of Credit Facility [Line Items]
Long-term debt				$ 2,180,847				$ 1,603,772
United States Dollar Revolving Loan [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Long-term debt								$ 11,000
Debt instrument, interest rate, stated percentage						1.67%	1.67%	1.67%	1.67%
Australian dollar (swingline loan) [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Long-term debt	AUD 3,000			$ 2,186		AUD 8,000		$ 6,538
Debt instrument, interest rate, stated percentage	6.11%	6.11%	6.11%	6.11%	6.11%	6.44%	6.44%	6.44%	6.44%
British Pound Revolving Loan [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Long-term debt		£ 5,500		$ 8,109
Debt instrument, interest rate, stated percentage	2.51%	2.51%	2.51%	2.51%	2.51%
Canadian Dollar Revolving Loan [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Long-term debt				$ 24,200	CAD 33,500			$ 20,688	CAD 24,000
Debt instrument, interest rate, stated percentage	2.87%	2.87%	2.87%	2.87%	2.87%	2.79%	2.79%	2.79%	2.79%
Euro Revolving Loan [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Long-term debt			€ 9,500	$ 10,317			€ 4,100	$ 4,961
Debt instrument, interest rate, stated percentage	2.00%	2.00%	2.00%	2.00%	2.00%	1.51%	1.51%	1.51%	1.51%