Segment Information - Revenue by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Summary of revenue by segment
Revenue	$ 129,936	$ 123,725
Operating Segments | Radiology
Summary of revenue by segment
Revenue	87,812	85,639
Operating Segments | Oncology
Summary of revenue by segment
Revenue	30,033	26,062
Operating Segments | Interventional
Summary of revenue by segment
Revenue	11,652	11,663
Operating Segments | MRI | Radiology
Summary of revenue by segment
Revenue	49,455	47,570
Operating Segments | PET/CT | Radiology
Summary of revenue by segment
Revenue	32,180	31,666
Operating Segments | Other Radiology | Radiology
Summary of revenue by segment
Revenue	6,177	6,403
Corporate / Other
Summary of revenue by segment
Revenue	$ 439	$ 361