Note 8 - Contract Balance - Summary of Deferred Service Contract Revenue (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Beginning Balance, deferred service contract revenue	$ 11,807	$ 10,013	$ 11,656	$ 9,431
Add: Payments received	3,609	3,178	12,025	10,290
Less: Revenue recognized	(4,097)	(3,233)	(12,362)	(9,763)
Ending Balance, deferred service contract revenue	$ 11,319	$ 9,958	$ 11,319	$ 9,958

Amount of deferred revenue recognized for transactions arising during the current reporting period. Deferred revenue is a liability as of the balance sheet date related to a revenue producing activity for which revenue has not yet been recognized. Generally, an Entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

No definition available.

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