Fair Value of Financial Instruments Financial Instruments Carried at Historical Cost (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 2,391,633	$ 2,256,312
Long-term debt, Fair Value	2,406,601	2,279,901
Revolving credit facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	160,033	225,155
Long-term debt, Fair Value	163,662	229,483
Other debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	2,356	2,419
Long-term debt, Fair Value	2,352	2,426
Credit Agreement [Member] | United States Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	1,295,672	1,204,714
Long-term debt, Fair Value	1,296,079	1,208,657
Credit Agreement [Member] | U.K. term loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	315,524	124,747
Long-term debt, Fair Value	319,556	126,480
Australia Credit Agreement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	450,252	513,192
Long-term debt, Fair Value	457,978	528,105
MIRA Partner Loan Agreement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	167,796	186,085
Long-term debt, Fair Value	$ 166,974	$ 184,750