Note 9 - Fair Value Measurement - Schedule of Carrying and Fair Value Amounts (Details) - USD ($) $ in Thousands		Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Reported Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Held-to-maturity marketable securities (1)	[1]	$ 10,850	$ 5,200	$ 5,896
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
2.75% Convertible Notes	[2],[3]	203,771	200,303	196,946
Reported Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Revolving Credit Facility [Member]
Credit Agreement - revolving credit facility	[3]	0	0	75,000
Reported Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Term Loan [Member]
Credit Agreement - term loan	[3]	127,500	131,250	135,000
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Held-to-maturity marketable securities (1)	[1]	10,801	5,200	5,896
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
2.75% Convertible Notes	[2],[3]	333,500	248,400	184,554
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member] | Revolving Credit Facility [Member]
Credit Agreement - revolving credit facility	[3]	0	0	76,291
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member] | Term Loan [Member]
Credit Agreement - term loan	[3]	$ 128,639	$ 133,030	$ 137,116

[1] All marketable securities were classified as held-to-maturity and consisted of U.S. Government and agency obligations maturing in one to five years.

[2] Excluded from the carrying value is debt discount of $26.2 million, $29.7 million and $33.1 million as of June 30, 2021, December 31, 2020 and June 30, 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. 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.