Property and Equipment - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 99,054	$ 96,941
Accumulated depreciation	(58,753)	(55,461)
Property and equipment, net	40,301	41,480
Medical equipment and facilities
Property, Plant and Equipment [Line Items]
Property and equipment, gross	94,200	92,132
Office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	604	594
Deposits and construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,000	1,965
Deposits towards purchase of proton beam systems
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,250	$ 2,250