Note 6 - Contract Assets and Contract Liabilities (Details Textual)	3 Months Ended
Mar. 31, 2018 USD ($)
Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Modification of Contract	$ 282,000
Contract with Customer, Liability, Revenue Recognized	$ 330,000

Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from contract modification which increases (decreases) 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045

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