Florida Oncology Partners (Details)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2018 shares	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) Term	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($)	Sep. 22, 2017 USD ($)
Florida Oncology Partners [Abstract]
Lease obligation		$ 176,000		$ 176,000
Down payment of capital leases				814,000	$ 1,034,000
Investments in unconsolidated entities		276,000		276,000		$ 179,000
Recorded distribution				63,000	0
Condensed Income Statement Information [Abstract]
Patient revenue		662,000	$ 658,000	2,005,000	2,324,000
Rental income				7,000	0
USNC's equity in loss		(56,000)	(135,000)	(292,000)	(799,000)
Condensed Balance Sheet Information [Abstract]
Current assets		2,699,000		2,699,000		2,681,000
Total assets		4,415,000		4,415,000		4,997,000
Current liabilities		790,000		790,000		1,638,000
Total liabilities and deficit		$ 4,415,000		$ 4,415,000		4,997,000
FOP [Member]
Florida Oncology Partners [Abstract]
Lease term		7 years		7 years
Lease obligation		$ 17,600,000		$ 17,600,000				$ 5,800,000
Percentage of guarantee obligations								25.00%
Down payment of capital leases							$ 1,000,000
Monthly payments for capital leases							$ 172,000
Common stock awarded as a part of bankruptcy proceedings (in shares) | shares	10,820
Lease payments				0
Investments in unconsolidated entities		0		0		0
Recorded distribution				0		0
Outstanding amount		511,000		511,000		649,000
Outstanding amount, less allowances		493,000		493,000		588,000
Amount received				155,000
Due from related parties		$ 18,000		$ 18,000		61,000
Note bearing interest		6.00%		6.00%
Accrued interest		$ 99,000		$ 99,000		68,000
Allowance for accrued interest		$ 99,000		$ 99,000		68,000
FOP [Member] | Maximum [Member]
Florida Oncology Partners [Abstract]
Amount of guarantee obligation								$ 1,433,000
FOP [Member] | Office Space [Member]
Florida Oncology Partners [Abstract]
Lease term		10 years		10 years
Loan amount										$ 4,106,000
Outstanding Loan		$ 3,120,000		$ 3,120,000		3,273,000
Debt maturity period				7 years
FOP [Member] | Radiation Therapy Center [Member]
Florida Oncology Partners [Abstract]
Lease term		10 years		10 years
Lease obligation											$ 14,321,000
Monthly payments for capital leases		$ 167,000		$ 167,000					$ 160,000
Maximum number of additional terms extended | Term				3
Extension of agreement				5 years
Percentage of increase of monthly payments each year				2.00%
FOP [Member] | Letter of Credit [Member] | Office Space [Member]
Florida Oncology Partners [Abstract]
Letter of credit, amount		$ 88,000		$ 88,000
FOP [Member] | USNC [Member]
Florida Oncology Partners [Abstract]
Ownership percentage		24.00%		24.00%
FOP [Member] | Investment in Unconsolidated Entity [Member]
Condensed Income Statement Information [Abstract]
Patient revenue		$ 0	0	$ 0	1,922,000
Rental income		0	181,000	0	543,000
Net loss		(44,000)	(114,000)	(7,000)	(705,000)
USNC's equity in loss		(11,000)	$ (280,000)	(2,000)	$ (171,000)
Condensed Balance Sheet Information [Abstract]
Current assets		165,000		165,000		165,000
Noncurrent assets		1,120,000		1,120,000		1,202,000
Total assets		1,285,000		1,285,000		1,367,000
Current liabilities		4,018,000		4,018,000		4,003,000
Noncurrent liabilities		1,001,000		1,001,000		1,091,000
Deficit		(3,734,000)		(3,734,000)		(3,727,000)
Total liabilities and deficit		$ 1,285,000		$ 1,285,000		$ 1,367,000