Note 6 - Investments - Securities Lending Agreements (Details) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Securities Financing Transaction [Line Items]
Securities Lending Rate of Collateral Required	1.02
Foreign government and agency securities
Securities Financing Transaction [Line Items]
Securities Lending Rate of Collateral Required	1.05
Securities Financing Transaction, Fair Value
Securities Financing Transaction [Line Items]
Securities Lending Rate of Collateral Required	1
Securities Received as Collateral	$ 43.3	$ 42.4

The carrying value as of the balance sheet date of the assets received as collateral against securities loaned to other broker-dealers. Borrowers of securities generally are required to provide collateral to the lenders of securities, commonly cash but sometimes other securities or standby letters of credit, with a value slightly higher than that of the securities borrowed. In instances where the entity is permitted to sell or re-pledge these securities, the entity reports the fair value of the collateral received and the related obligation to return the collateral as a liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Name:	us-gaap_SecuritiesReceivedAsCollateral
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant