Note 3 - Revenue From Contracts With Customers - Impact of New Standard on Condensed Consolidated Balance Sheet and Condensed Consolidated Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Total revenues	$ 21,966	$ 17,844
Cost of revenues	15,389	12,160
Gross profit	6,577	5,684
Profit (loss) from operations	(3,779)	(4,010)
Loss before taxes	(3,563)	(4,080)
Income tax benefit	(302)	(226)
Net loss	$ (3,261)	$ (3,854)
Basic and diluted loss per common share (in dollars per share)	$ (0.11)	$ (0.18)
Assets
Inventories	$ 11,906		$ 12,828	$ 13,892
Contract assets	1,196		1,783	2,299
Prepaid expenses and other	1,691			1,606
Total current assets	36,423		39,696	41,276
Segment assets	83,925	$ 78,903	86,329	87,909
Liabilities
Contract liabilities	5,168		4,661	8,829
Refund liabilities	1,951		1,565	695
Total current liabilities	16,154		15,616	18,914
Deferred tax liabilities	1,999		2,241	2,414
Total liabilities	27,150		26,952	30,423
Stockholders' Equity
Accumulated deficit	(109,929)		(106,668)	(108,559)
Accumulated other comprehensive loss	(3,071)			(3,510)
Total stockholders' equity	56,775		59,377	57,486
Total liabilities and stockholders' equity	83,925		$ 86,329	87,909
Accounting Standards Update 2014-09 [Member]
Assets
Inventories				(1,064)
Contract assets				(516)
Total current assets				(1,580)
Segment assets				(1,580)
Liabilities
Contract liabilities				(4,168)
Refund liabilities				870
Total current liabilities				(3,298)
Deferred tax liabilities				(173)
Total liabilities				(3,471)
Stockholders' Equity
Accumulated deficit				1,891
Total stockholders' equity				1,891
Total liabilities and stockholders' equity				$ (1,580)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Total revenues	21,704
Cost of revenues	15,746
Gross profit	5,958
Profit (loss) from operations	(4,398)
Loss before taxes	(4,182)
Income tax benefit	(391)
Net loss	$ (3,791)
Basic and diluted loss per common share (in dollars per share)	$ (0.13)
Assets
Inventories	$ 12,548
Contract assets	1,570
Prepaid expenses and other	1,780
Total current assets	37,528
Segment assets	85,030
Liabilities
Contract liabilities	9,621
Refund liabilities	819
Total current liabilities	19,475
Deferred tax liabilities	2,178
Total liabilities	30,650
Stockholders' Equity
Accumulated deficit	(112,350)
Accumulated other comprehensive loss	(3,045)
Total stockholders' equity	54,380
Total liabilities and stockholders' equity	85,030
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Total revenues	262
Cost of revenues	(357)
Gross profit	619
Profit (loss) from operations	619
Loss before taxes	619
Income tax benefit	89
Net loss	$ 530
Basic and diluted loss per common share (in dollars per share)	$ 0.02
Assets
Inventories	$ (642)
Contract assets	(374)
Prepaid expenses and other	(89)
Total current assets	(1,105)
Segment assets	(1,105)
Liabilities
Contract liabilities	(4,453)
Refund liabilities	1,132
Total current liabilities	(3,321)
Deferred tax liabilities	(179)
Total liabilities	(3,500)
Stockholders' Equity
Accumulated deficit	2,421
Accumulated other comprehensive loss	(26)
Total stockholders' equity	2,395
Total liabilities and stockholders' equity	$ (1,105)