Note 4 - Revenue From Contracts With Customers (Details Textual) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Contract with Customer, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price and Input Costs	$ (172,000)	$ 909,000
Increase (Decrease) in Contract with Customer, Asset	$ (268,884)	$ (4,677,663)

Amount of increase (decrease) in right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Name:	us-gaap_IncreaseDecreaseInContractWithCustomerAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration