Note 13 - Commitments and Contingencies (Details Textual)		12 Months Ended
	Sep. 05, 2017	Dec. 31, 2021 USD ($)
Number Of Purchase Commitments		2
Leksell Gamma Knife Icon Systems and Linear Accelerator System [Member]
Long-term Install Service and Purchase Commitment, Amount		$ 10,760,000
Long-term Commitment, Cash on Hand to Fund		8,263,000
Long-term Commitment, Line of Credit to Fund		$ 7,000,000
LINAC System [Member] | Maximum [Member]
Long-Term Service Commitment, Period (Year)		9 years
LINAC System [Member] | Minimum [Member]
Long-Term Service Commitment, Period (Year)		5 years
Long-Term Service Commitment, Amount		$ 8,408,000
Mevion PBRT Units [Member] | Upgrade and Purchase MEVION Systems [Member]
Long-term Purchase Commitment, Amount		34,000,000
Mevion Medical Systems Inc [Member] | Maintenance And Support Agreement, Mevion Service Agreement [Member]
Long-term Purchase Commitment, Renewal Term (Year)	5 years
Purchase Agreement Annual Prepayment		$ 1,649,000
Long-term Purchase Commitment, Period (Year)	1 year