Note 6 - Fair Value Measurement and Financial Instruments (Details) - Assets and Liabilities Measured at Fair Value Measured on a Recurring Basis (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Assets:
Asset Fair Value	$ 27,971	$ 47,137
Liabilities:
Liability Fair Value	84	1,085
Warrant Liability [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities:
Liability Fair Value		883
Warrant Liability [Member]
Liabilities:
Liability Fair Value		883
Stock-based Compensation Liability [Member] | Fair Value, Inputs, Level 3 [Member]
Liabilities:
Liability Fair Value	84	202
Stock-based Compensation Liability [Member]
Liabilities:
Liability Fair Value	84	202
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Assets:
Asset Fair Value	1,793	55
Fair Value, Inputs, Level 1 [Member]
Assets:
Asset Fair Value	1,793	55
Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]
Assets:
Asset Fair Value	21,297	23,570
Fair Value, Inputs, Level 2 [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Assets:
Asset Fair Value	2,006	17,005
Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Assets:
Asset Fair Value	2,875	6,507
Fair Value, Inputs, Level 2 [Member]
Assets:
Asset Fair Value	26,178	47,082
Fair Value, Inputs, Level 3 [Member]
Liabilities:
Liability Fair Value	84	1,085
Money Market Funds [Member]
Assets:
Asset Fair Value	1,793	55
Commercial Paper [Member]
Assets:
Asset Fair Value	21,297	23,570
US Government-sponsored Enterprises Debt Securities [Member]
Assets:
Asset Fair Value	2,006	17,005
Corporate Debt Securities [Member]
Assets:
Asset Fair Value	$ 2,875	$ 6,507