Boca Oncology Partners (Details)	1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 30, 2012	Jun. 30, 2011 USD ($)	Sep. 30, 2020 USD ($) ft²	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) ft²	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Boca Oncology Partners [Abstract]
Recorded investments			$ 276,000		$ 276,000		$ 179,000
Recorded distribution					63,000	$ 0
Condensed Income Statement Information [Abstract]
Rental income					7,000	0
USNC's equity in earnings (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 equity			$ 4,415,000		$ 4,415,000		$ 4,997,000
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
Outstanding balance on mortgage			$ 3,129,000		$ 3,129,000
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			21.22%		21.22%		21.22%
Recorded investments			$ 142,000		$ 142,000		$ 179,000
Recorded distribution					43,000
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	0	0
Net income (loss)			30,000	(4,000)	37,000	(4,000)
USNC's equity in earnings (loss)			7,000	$ (1,000)	8,000	$ (1,000)
Condensed Balance Sheet Information [Abstract]
Current assets			71,000		71,000		64,000
Noncurrent assets			757,000		757,000		935,000
Total assets			828,000		828,000		999,000
Current liabilities			0		0		0
Noncurrent liabilities			0		0		0
Equity			828,000		828,000		999,000
Total liabilities and equity			$ 828,000		$ 828,000		$ 999,000
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%