Note 4 - Fair Value Measurements - Fair Value of Assets and Liabilities Measured On Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Cash and cash equivalents	$ 16,437	$ 25,028
Restricted cash equivalents		25
Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	16,437	25,028
Restricted cash equivalents		25
Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	0	0
Restricted cash equivalents		0
Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents	$ 0	0
Restricted cash equivalents		$ 0

Fair value portion of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

No definition available.

Name:	sfe_RestrictedCashAndCashEquivalentsFairValue
Namespace Prefix:	sfe_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant