Note 9 - Fair Value Measurement - Schedule of Carrying and Fair Value Amounts (Details) - USD ($) $ in Thousands		Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Held-to-maturity marketable securities (1)	[1]	$ 11,300	$ 5,200	$ 5,000
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
2.75% Convertible Notes	[2],[3]	202,018	200,303	195,295
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Revolving Credit Facility [Member]
Credit Agreement - revolving credit facility	[3]	0	0	25,000
Reported Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Term Loan [Member]
Notes	[3]	129,375	131,250	136,875
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Held-to-maturity marketable securities (1)	[1]	11,258	5,200	5,006
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
2.75% Convertible Notes	[2],[3]	324,013	248,400	176,094
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Revolving Credit Facility [Member]
Credit Agreement - revolving credit facility	[3]	0	0	25,061
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Term Loan [Member]
Notes	[3]	$ 130,645	$ 133,030	$ 137,194

[1] All marketable securities were classified as held-to-maturity and consisted of U.S. Government and agency obligations as of March 31, 2021, December 31, 2020 and March 31, 2020.

[2] Excluded from the carrying value is debt discount of $ 28.0 million, $ 29.7 million and $ 34.7 million as of March 31, 2021 , December 31, 2020 and March 31, 2020, respectively, related to the 2.75% Convertible Notes (see Note 13).

[3] The fair value of the 2.75% Convertible Notes is based on the median price of the notes in an active market as of March 31, 2021 , December 31, 2020 and March 31, 2020. The fair value of the Credit Agreement is based on borrowing rates available to us for long-term loans with similar terms, average maturities, and credit risk. See Note 13 for more information about the Credit Agreement and 2.75% Convertible Notes.