Fair Value Measurements (Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	$ 1,329,998	$ 1,385,632
Senior notes (Level 1) | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	526,131	745,943
Revolving credit facilities and term loans (Level 2) | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	803,867	639,689
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	1,332,311	1,364,429
Carrying Value | Senior notes (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	524,978	723,867
Carrying Value | Revolving credit facilities and term loans (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments	$ 807,333	$ 640,562