Investments in Unconsolidated Entities, The Southern California Regional Gamma Knife Center (Details)		3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Apr. 01, 2016 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Jun. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) Payment	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Feb. 29, 2016 USD ($)
The Southern California Regional Gamma Knife Center [Abstract]
Renovation installation and operation agreement period								14 years
Lease payment								$ 89,000	$ 901,000
Condensed Income Statement Information [Abstract]
Patient revenue		$ 0	$ 0	$ 0	$ 1,061,000	$ 1,061,000	$ 1,061,000	1,061,000	3,173,000
Net (loss) income		(296,000)	(352,000)	(617,000)	292,000	(325,000)	(677,000)	(973,000)	533,000
USNC's equity in (loss) income		(119,000)	(77,000)	(135,000)	(139,000)	(274,000)	(351,000)	(470,000)	(809,000)
Condensed Balance Sheet Information [Abstract]
Current assets		2,243,000	2,634,000	2,909,000	3,451,000	2,909,000	2,634,000	2,243,000	3,007,000
Total assets		3,688,000	3,772,000	4,073,000	4,614,000	4,073,000	3,772,000	3,688,000	4,173,000
Current liabilities		626,000	718,000	656,000	569,000	656,000	718,000	626,000	410,000
Noncurrent liabilities			45,000	56,000	67,000	56,000	45,000
Equity		3,028,000	3,009,000	3,361,000	3,978,000	3,361,000	3,009,000	3,028,000	3,686,000	$ 3,153,000
Total liabilities and equity		3,688,000	$ 3,772,000	$ 4,073,000	$ 4,614,000	$ 4,073,000	$ 3,772,000	3,688,000	4,173,000
Neuro Partners LLC and CGK [Member]
The Southern California Regional Gamma Knife Center [Abstract]
Recorded amount of equity method income								(10,000)	26,000
Neuro Partners LLC and CGK [Member] | Investment in Unconsolidated Entity [Member]
Condensed Income Statement Information [Abstract]
Patient revenue								606,000	1,141,000
Net (loss) income								(9,000)	391,000
USNC's equity in (loss) income								(36,000)	124,000
Condensed Balance Sheet Information [Abstract]
Current assets		299,000						299,000	121,000
Noncurrent assets		294,000						294,000	551,000
Total assets		593,000						593,000	672,000
Current liabilities		564,000						564,000	634,000
Noncurrent liabilities		0						0	0
Equity		29,000						29,000	38,000
Total liabilities and equity		$ 593,000						$ 593,000	672,000
Neuro Partners LLC [Member]
The Southern California Regional Gamma Knife Center [Abstract]
Ownership percentage		20.00%						20.00%
Neuro Partners LLC [Member] | Lease One [Member]
The Southern California Regional Gamma Knife Center [Abstract]
Share of guarantee in lease obligation								20.00%
Lease term		7 years						7 years
Lease obligation											$ 668,000
Neuro Partners LLC [Member] | Lease Two [Member]
The Southern California Regional Gamma Knife Center [Abstract]
Lease term		5 years						5 years
Lease obligation											$ 1,663,000
Number of lease payments | Payment								60
Lease payment	$ 31,000
CGK [Member]
The Southern California Regional Gamma Knife Center [Abstract]
Ownership percentage		39.00%						39.00%
Due from related parties		$ 6,000						$ 6,000	$ 9,000