Entity Wide Disclosures - Summary of Revenue by Major Source (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Line Items]
Total revenue	$ 200,741	$ 163,077
Oncology
Disaggregation Of Revenue [Line Items]
Total revenue	55,962	43,853
Other
Disaggregation Of Revenue [Line Items]
Total revenue	51,319	34,217
Metabolic
Disaggregation Of Revenue [Line Items]
Total revenue	33,742	28,513
Cardiology
Disaggregation Of Revenue [Line Items]
Total revenue	20,424	23,736
AVAI
Disaggregation Of Revenue [Line Items]
Total revenue	19,924	16,679
Central Nervous System
Disaggregation Of Revenue [Line Items]
Total revenue	14,868	13,165
Medical Devices
Disaggregation Of Revenue [Line Items]
Total revenue	$ 4,502	$ 2,914