Segment Information - Revenue by Segment (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 revenue by segment
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 revenue by segment
Revenue									339,627	343,463	370,968
Oncology
Summary of revenue by segment
Revenue									99,957	$ 92,924	$ 77,863
Corporate / Other
Summary of revenue by segment
Revenue									$ 33,470