Note 8 - Contract Balance - Summary of Deferred Service Contract Revenue (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Beginning Balance, deferred service contract revenue	$ 11,015	$ 9,555	$ 11,656	$ 9,431
Add: Payments received	4,739	3,721	8,416	7,112
Less: Revenue recognized	(3,947)	(3,263)	(8,265)	(6,530)
Ending Balance, deferred service contract revenue	$ 11,807	$ 10,013	$ 11,807	$ 10,013

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