Segment Information - Components of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of components of revenue
Revenue	$ 124,337	$ 120,784	$ 118,504	$ 109,429	$ 109,647	$ 110,137	$ 111,238	$ 105,365	$ 473,054	$ 436,387	$ 448,831
Radiology
Summary of components of revenue
Revenue									339,627	343,463	370,968
Oncology
Summary of components of revenue
Revenue									99,957	92,924	77,863
Corporate / Other
Summary of components of revenue
Revenue									33,470
MRI | Radiology
Summary of components of revenue
Revenue									183,893	180,815	187,207
PET/CT | Radiology
Summary of components of revenue
Revenue									128,356	133,224	145,027
Other Radiology
Summary of components of revenue
Revenue									$ 27,378	$ 29,425	$ 38,734