Note 4 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Money market funds	$ 122,351	$ 137,340
Total assets	122,351	137,340
Business Combination, Contingent Consideration, Liability, Noncurrent	16,100	14,200
Total liabilities	16,100	14,200
Fair Value, Inputs, Level 1 [Member]
Money market funds	122,351	137,340
Total assets	122,351	137,340
Business Combination, Contingent Consideration, Liability, Noncurrent
Total liabilities
Fair Value, Inputs, Level 2 [Member]
Money market funds
Total assets
Business Combination, Contingent Consideration, Liability, Noncurrent
Total liabilities
Fair Value, Inputs, Level 3 [Member]
Money market funds
Total assets
Business Combination, Contingent Consideration, Liability, Noncurrent	16,100	14,200
Total liabilities	$ 16,100	$ 14,200