Note 4 - Fair Value Measurements - Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Cash equivalents	$ 69,102	$ 61,635
Investments	20,500	27,751
Fair Value, Inputs, Level 1 [Member]
Cash equivalents
Investments
Fair Value, Inputs, Level 2 [Member]
Cash equivalents	69,102	61,635
Investments		27,751
Fair Value, Inputs, Level 3 [Member]
Cash equivalents
Investments
Money Market Funds [Member]
Cash equivalents	68,352	61,385
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents	68,352	61,385
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Cash equivalents
Certificates of Deposit [Member]
Cash equivalents	750	250
Investments	20,500	25,750
Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member]
Cash equivalents
Investments
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member]
Cash equivalents	750	250
Investments	20,500	25,750
Certificates of Deposit [Member] | Fair Value, Inputs, Level 3 [Member]
Cash equivalents
Investments
Corporate Debt Securities [Member]
Investments		2,001
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Investments
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Investments		2,001
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Investments