Note 7 - Letters of Credit (Details Textual) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Letters of Credit Outstanding, Amount	$ 1.2	$ 1.2
Letter of Credit [Member]
Line of Credit Facility, Commitment Fee Percentage	1.00%	1.00%

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

No definition available.

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration