Note 2 - Summary of Significant Accounting Policies - Impact of New Standard on Condensed Consolidated Balance Sheet and Condensed Consolidated Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Dec. 31, 2015
Total revenues	$ 96,789	$ 83,275	$ 86,461
Cost of revenues	67,879	55,406	54,200
Gross profit	28,910	27,869	32,261
Income (loss) from operations	(16,778)	(13,929)	(6,510)
Loss before taxes	(17,531)	(14,195)	(7,228)
Income tax (benefit) expense	(206)	(1,606)	38
Net loss	$ (17,325)	$ (12,589)	$ (7,266)
Basic and diluted loss per common share (in dollars per share)	$ (0.61)	$ (0.56)	$ (0.35)
Assets:
Inventories	$ 13,042	$ 13,892		$ 12,828
Contract assets	1,744	2,299		1,783
Total current assets	35,481	41,276		39,696
Total assets	70,167	87,909	$ 79,843	86,329
us-gaap_LiabilitiesAbstract
Contract liabilities	2,226	8,829		4,661
Refund liabilities	2,417	695		1,565
Total current liabilities	18,586	18,914		15,616
Deferred tax liabilities	1,922	2,414		2,241
Total liabilities	28,629	30,423		26,952
Stockholders' Equity:
Accumulated deficit	(123,993)	(108,559)		(106,668)
Total stockholders' equity	41,538	59,377	$ 48,635	59,377	$ 59,516
Total liabilities and stockholders' equity	70,167	87,909		$ 86,329
Accounting Standards Update 2014-09 [Member]
Assets:
Inventories		(1,064)
Contract assets		(516)
Total current assets		(1,580)
Total assets		(1,580)
us-gaap_LiabilitiesAbstract
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	91,417
Cost of revenues	64,495
Gross profit	26,922
Income (loss) from operations	(18,766)
Loss before taxes	(19,519)
Income tax (benefit) expense	(462)
Net loss	$ (19,057)
Basic and diluted loss per common share (in dollars per share)	$ (0.67)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Assets:
Inventories	$ (4,536)
Contract assets	(365)
Total current assets	(4,901)
Total assets	(4,901)
us-gaap_LiabilitiesAbstract
Contract liabilities	(9,977)
Refund liabilities	1,354
Total current liabilities	(8,623)
Deferred tax liabilities	99
Total liabilities	(8,524)
Stockholders' Equity:
Accumulated deficit	3,623
Total stockholders' equity	3,623
Total liabilities and stockholders' equity	(4,901)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Total revenues	5,372
Cost of revenues	3,384
Gross profit	1,988
Income (loss) from operations	1,988
Loss before taxes	1,988
Income tax (benefit) expense	256
Net loss	$ 1,732
Basic and diluted loss per common share (in dollars per share)	$ 0.06
Assets:
Inventories	$ 17,578
Contract assets	2,109
Total current assets	40,382
Total assets	75,068
us-gaap_LiabilitiesAbstract
Contract liabilities	12,203
Refund liabilities	1,063
Total current liabilities	27,209
Deferred tax liabilities	1,823
Total liabilities	37,153
Stockholders' Equity:
Accumulated deficit	(127,616)
Total stockholders' equity	37,915
Total liabilities and stockholders' equity	$ 75,068