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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Total revenues	$ 24,744	$ 21,796	$ 69,837	$ 62,141
Cost of revenues	16,482	14,356	47,363	40,793
Gross profit	8,262	7,440	22,474	21,348
Profit (loss) from operations	(1,484)	(2,019)	(9,432)	(7,679)
Loss before taxes	(1,677)	(2,079)	(9,841)	(7,884)
Net loss	$ (1,534)	$ (1,902)	$ (9,561)	$ (7,324)
Basic and diluted loss per common share (in dollars per share)	$ (0.05)	$ (0.09)	$ (0.34)	$ (0.35)
Income tax benefit	$ (143)	$ (177)	$ (280)	$ (560)
Assets
Inventories	16,052		16,052		$ 12,828	$ 13,892
Contract assets	1,575		1,575		1,783	2,299
Total current assets	34,597		34,597		39,696	41,276
Segment assets	78,957	$ 79,577	78,957	$ 79,577	86,329	87,909
Liabilities
Accrued expenses	4,528		4,528			4,186
Current contract liabilities	3,657		3,657		4,661	8,829
Refund liabilities	2,518		2,518		1,565	695
Total current liabilities	18,447		18,447		15,616	18,914
Total liabilities	29,242		29,242		26,952	30,423
Stockholders' Equity
Accumulated deficit	(116,229)		(116,229)		(106,668)	(108,559)
Accumulated other comprehensive loss	(3,940)		(3,940)			(3,510)
Total stockholders' equity	49,715		49,715		59,377	57,486
Total liabilities and stockholders' equity	78,957		78,957		$ 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
Current contract liabilities						(4,168)
Refund liabilities						870
Total current liabilities						(3,298)
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	23,581		67,080
Cost of revenues	15,799		46,248
Gross profit	7,782		20,832
Profit (loss) from operations	(1,964)		(11,074)
Loss before taxes	(2,157)		(11,483)
Net loss	$ (2,014)		$ (11,030)
Basic and diluted loss per common share (in dollars per share)	$ (0.07)		$ (0.39)
Income tax benefit			$ (453)
Assets
Inventories	$ 18,212		18,212
Contract assets	2,534		2,534
Total current assets	37,716		37,716
Segment assets	82,076		82,076
Liabilities
Accrued expenses	4,441		4,441
Current contract liabilities	11,772		11,772
Refund liabilities	976		976
Total current liabilities	24,933		24,933
Total liabilities	35,728		35,728
Stockholders' Equity
Accumulated deficit	(119,589)		(119,589)
Accumulated other comprehensive loss	(3,947)		(3,947)
Total stockholders' equity	46,348		46,348
Total liabilities and stockholders' equity	82,076		82,076
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Total revenues	1,163		2,757
Cost of revenues	683		1,115
Gross profit	480		1,642
Profit (loss) from operations	480		1,642
Loss before taxes	480		1,642
Net loss	$ 480		$ 1,469
Basic and diluted loss per common share (in dollars per share)	$ 0.02		$ 0.05
Income tax benefit			$ 173
Assets
Inventories	$ (2,160)		(2,160)
Contract assets	(959)		(959)
Total current assets	(3,119)		(3,119)
Segment assets	(3,119)		(3,119)
Liabilities
Accrued expenses	87		87
Current contract liabilities	(8,115)		(8,115)
Refund liabilities	1,542		1,542
Total current liabilities	(6,486)		(6,486)
Total liabilities	(6,486)		(6,486)
Stockholders' Equity
Accumulated deficit	3,360		3,360
Accumulated other comprehensive loss	7		7
Total stockholders' equity	3,367		3,367
Total liabilities and stockholders' equity	$ (3,119)		$ (3,119)