Investments in Unconsolidated Entities, Boca Oncology Partners (Details)	1 Months Ended		3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011 USD ($)	Dec. 31, 2021 USD ($) ft²	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Jun. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) ft²	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Boca Oncology Partners [Abstract]
Investments in unconsolidated entities			$ 141,000	$ 152,000	$ 164,000	$ 161,000	$ 164,000	$ 152,000	$ 141,000	$ 160,000
Condensed Income Statement Information [Abstract]
Rental income										7,000
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
USNC [Member] | Boca West IMP [Member]
Boca Oncology Partners [Abstract]
Share of guarantee in mortgage			10.00%						10.00%
Share of guarantee in outstanding mortgage			50.00%						50.00%
Mortgage term of guarantee									10 years
Original balance of mortgage			$ 3,000,000						$ 3,000,000
Boca Oncology Partners, LLC [Member]
Boca Oncology Partners [Abstract]
Area of real estate property (in square foot) | ft²			6,000						6,000
Boca Oncology Partners RE, LLC ("BOPRE") [Member]
Boca Oncology Partners [Abstract]
Ownership percentage			22.50%						22.50%
Investments in unconsolidated entities			$ 151,000						$ 151,000	134,000
Boca Oncology Partners RE, LLC ("BOPRE") [Member] | Boca West IMP [Member]
Boca Oncology Partners [Abstract]
Percentage of interest in medical office building		20.00%
Ownership percentage	23.75%
Additional investor purchased ownership percentage	3.75%
Boca Oncology Partners RE, LLC ("BOPRE") [Member] | Investment in Unconsolidated Entity [Member]
Condensed Income Statement Information [Abstract]
Rental income									0	0
Net (loss) income									85,000	63,000
USNC's equity in (loss) income									17,000	13,000
Condensed Balance Sheet Information [Abstract]
Current assets			112,000						112,000	27,000
Noncurrent assets			757,000						757,000	757,000
Total assets			869,000						869,000	784,000
Current liabilities			0						0	0
Noncurrent liabilities			0						0	0
Equity			869,000						869,000	784,000
Total liabilities and equity			$ 869,000						$ 869,000	$ 784,000
BOP and BOPRE [Member]
Boca Oncology Partners [Abstract]
Area of real estate property (in square foot) | ft²			32,000						32,000
Investments in unconsolidated entities		$ 225,000
Ownership percentage		22.50%