Note 6 - Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]
Assets:
Certificate of deposit	$ 225	$ 225
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Cash and cash equivalents	12,383	38,722
Total assets	12,608	38,947
Liabilities:
Common stock warrant liability
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Assets:
Certificate of deposit
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Cash and cash equivalents
Total assets
Liabilities:
Common stock warrant liability
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit [Member]
Assets:
Certificate of deposit
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Cash and cash equivalents
Total assets
Liabilities:
Common stock warrant liability		223
Fair Value, Measurements, Recurring [Member] | Certificates of Deposit [Member]
Assets:
Certificate of deposit	225	225
Fair Value, Measurements, Recurring [Member]
Assets:
Cash and cash equivalents	12,383	38,722
Total assets	12,608	38,947
Liabilities:
Common stock warrant liability		223
Common stock warrant liability		$ 223