Note 7 - Debt, Credit Facility and Leases - Debt Summary (Details) - Senior Notes [Member] - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Principal	$ 513,918	$ 512,886
Unamortized discount/premium and issuance costs	(5,307)	(5,644)
Long-term debt balance	508,611	507,242
The 2028 Senior Notes [Member]
Principal	475,000	475,000
Unamortized discount/premium and issuance costs	(6,007)	(6,462)
Long-term debt balance	468,993	468,538
IQ Notes [Member]
Principal	38,918	37,886
Unamortized discount/premium and issuance costs	700	818
Long-term debt balance	$ 39,618	$ 38,704