Note 2 - Summary of Significant Accounting Policies - Cumulative Effect of Adjustments for New Accounting Pronouncements on Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets:
Inventories	$ 13,042	$ 12,828	$ 13,892
Contract assets	1,744	1,783	2,299
Total current assets	35,481	39,696	41,276
Total assets	70,167	86,329	87,909	$ 79,843
us-gaap_LiabilitiesAbstract
Contract liabilities	2,226	4,661	8,829
Refund liabilities	2,417	1,565	695
Total current liabilities	18,586	15,616	18,914
Deferred tax liabilities	1,922	2,241	2,414
Total liabilities	28,629	26,952	30,423
Stockholders' Equity:
Retained Earnings (Accumulated Deficit), Ending Balance	(123,993)	(106,668)	(108,559)
Total stockholders' equity	41,538	59,377	59,377	$ 48,635	$ 59,516
Total liabilities and stockholders' equity	$ 70,167	$ 86,329	87,909
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:
Retained Earnings (Accumulated Deficit), Ending Balance			1,891
Total stockholders' equity			1,891
Total liabilities and stockholders' equity			(1,580)
Accounting Standards Update 2014-09 [Member] | Previously Reported [Member]
Stockholders' Equity:
Total stockholders' equity			$ 57,486