Property and Equipment - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 93,729	$ 96,941
Accumulated depreciation	(54,943)	(55,461)
Net property and equipment	38,786	41,480
Medical equipment and facilities
Property, Plant and Equipment [Line Items]
Property and equipment, gross	88,729	92,132
Office equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	339	594
Deposits and construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,411	1,965
Deposits towards purchase of proton beam systems
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,250	$ 2,250