Florida Oncology Partners (Details)	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($) shares	Mar. 31, 2021 USD ($) Term	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2011 USD ($)	Nov. 30, 2017 USD ($)	Sep. 22, 2017 USD ($)
Florida Oncology Partners [Abstract]
Down payment of capital leases		$ 89,000	$ 370,000
Recorded distribution		0	31,000
Investments in unconsolidated entities		161,000		$ 160,000
Condensed Income Statement Information [Abstract]
Income			2,000
USNC's equity in income (loss)		(139,000)	(146,000)
Condensed Balance Sheet Information [Abstract]
Current assets		3,451,000		3,007,000
TOTAL ASSETS		4,614,000		4,173,000
Current liabilities		322,000		410,000
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY		$ 4,614,000		4,173,000
FOP [Member]
Florida Oncology Partners [Abstract]
Lease term		7 years
Lease obligation		$ 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
Recorded distribution		0		0
Amount received				155,000
Lease payments		0
Investments in unconsolidated entities		$ 0		0
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
Loan amount							$ 4,106,000
Debt maturity period		7 years
Outstanding Loan		$ 2,994,000		3,066,000
FOP [Member] | Radiation Therapy Center [Member]
Florida Oncology Partners [Abstract]
Lease term		10 years
Lease obligation								$ 14,321,000
Monthly payments for capital leases	$ 160,000	$ 170,000
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
FOP [Member] | USNC [Member]
Florida Oncology Partners [Abstract]
Ownership percentage		24.00%
FOP [Member] | Investment in Unconsolidated Entity [Member]
Condensed Income Statement Information [Abstract]
Income		$ 0	0
Net loss		(41,000)	(52,000)
USNC's equity in income (loss)		(10,000)	$ (13,000)
Condensed Balance Sheet Information [Abstract]
Current assets		7,000		7,000
Noncurrent assets		1,064,000		1,091,000
TOTAL ASSETS		1,071,000		1,098,000
Current liabilities		4,112,000		4,068,000
Noncurrent liabilities		942,000		969,000
Deficit		(3,983,000)		(3,939,000)
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY		$ 1,071,000		1,098,000
21st Century Oncology [Member]
Florida Oncology Partners [Abstract]
Recorded distribution				$ 158,000