Note 8 - Stock-Based Compensation - Stock-based Compensation Allocation (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement, Expense	$ 14,794	$ 17,719	$ 9,396
Research and Development Expense [Member]
Share-based Payment Arrangement, Expense	10,222	13,977	6,867
Selling, General and Administrative Expenses [Member]
Share-based Payment Arrangement, Expense	$ 4,572	$ 3,742	$ 2,529

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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