Note 10 - Income Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount		$ 8,800	$ 9,800	$ 3,800
Operating Loss Carryforwards Attributable to Excess Stock Option Deductions		600
Tax Credit Carryforward, Amount		21,800	16,900	12,500
Operating Loss Carryforwards Excluded from Deferred Tax Assets		600
Unrecognized Tax Benefits		0	0	0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense		0	0	0
Scenario, Forecast [Member] | Increase to Deferred Tax Assets as Result of Adoption of ASU 2016-09 [Member]
Current Period Reclassification Adjustment	$ 600
Domestic Tax Authority [Member]
Operating Loss Carryforwards		101,400	94,200	78,300
Income Tax Expense (Benefit)		0	0	0
State and Local Jurisdiction [Member]
Operating Loss Carryforwards		53,000	46,400	55,100
Income Tax Expense (Benefit)		$ 0	$ 0	$ 0