Note 10 - Fair Value Disclosures - Fair Value of Financial Instruments (Details) - USD ($)		Dec. 31, 2019	Dec. 31, 2018
Senior notes, net		$ 304,832,000	$ 320,148,000
Unsecured revolving credit facility		0	67,500,000
Revolving Credit Facility [Member]
Unsecured revolving credit facility, carrying amount		0	67,500,000
Unsecured revolving credit facility		0	67,500,000
Senior Notes [Member] | Senior Notes Due 2022 [Member]
Senior notes, net	[1]	304,832,000	320,148,000
Senior Notes, fair value	[1]	$ 298,775,000	$ 292,500,000

[1] The carrying value for the Senior Notes, as presented at December 31, 2019, is net of the unamortized discount of $1.1 million, unamortized premium of $0.9 million, and unamortized debt issuance costs of $3.0 million. The carrying value of the Senior Notes, as presented at December 31, 2018, is net of the unamortized discount of $1.7 million, unamortized premium of $1.3 million, and unamortized debt issuance costs of $4.5 million. The unamortized discount, unamortized premium and debt issuance costs are not factored into the estimated fair value.