Note 6 - Redeemable, Convertible Preferred Stock (Details Textual) - USD ($)					6 Months Ended
	Mar. 30, 2021	Feb. 26, 2021	Feb. 25, 2021	Nov. 15, 2016	Jun. 30, 2021
Temporary Equity [Line Items]
Payments for repurchase of preferred stock					$ 100,000,000
Preferred stock, par value					$ 0
Series A Redeemable Preferred Stock [Member] | Purchase Agreement [Member]
Temporary Equity [Line Items]
Preferred stock, number of shares issued				2,000,000
Gross proceeds from issuance of shares				$ 200,000,000
Preferred stock, liquidation preference per share				$ 100
Purchase agreement date				Nov. 07, 2016
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, liquidation preference per share			$ 100
Percentage of cash dividend payable on preferred stock			4.00%
Carrying value of preferred stock at issuance		$ 93,000,000
Fair value of derivative liability		1,000,000
Transaction costs		$ 1,000,000
Preferred stock, redemption date		May 28, 2026
Temporary equity fair value of preferred stock at the time of issuance		$ 95,000,000
Common stock price equal or exceeds preferred stock conversion price		$ 14.50
Preferred stock conversion description					The Company will have the right to cause the mandatory conversion of the Series B Preferred Stock into shares of Common Stock at any time after the initial issuance of the Series B Preferred Stock if the closing price of the Common Stock has equaled or exceeded $14.50 (subject to adjustment in the same manner as the conversion price) for 45 trading days within a period of 60 consecutive trading days.
Fair value allocated to derivative liability					$ 1,000,000
Preferred stock, redemption price per share					$ 100
Series B Preferred Stock [Member] | Other Long-Term Liabilities [Member]
Temporary Equity [Line Items]
Fair value of derivative liability					$ 1,000,000
Series B Preferred Stock [Member] | Purchase Agreement [Member]
Temporary Equity [Line Items]
Initial conversion rate of preferred stock to common stock		9.5238
Initial conversion price of preferred stock per share of common stock		$ 10.50
Series B Preferred Stock [Member] | Repurchase and Exchange Agreement [Member]
Temporary Equity [Line Items]
Preferred stock, number of shares issued		1,000,000
Percentage of cash dividend payable on preferred stock		4.00%
Preferred stock, par value
Temporary equity exchange basis		one-for-one
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Stock repurchased		1,000,000
Percentage of cash dividend payable on preferred stock				5.50%
Net proceeds received to derivative liability				$ 43,000,000
Carrying value of preferred stock at issuance				155,000,000
Gross proceeds from preferred stock				200,000,000
Fair value of derivative liability				43,000,000
Transaction costs				$ 2,000,000
Preferred stock, redemption date				Nov. 15, 2021
Preferred stock prior to extinguishment carrying value including fair value of embedded derivative liability		$ 203,000,000
Temporary equity deemed preferred stock dividends		$ 8,000,000
Series A Preferred Stock [Member] | Repurchase and Exchange Agreement [Member]
Temporary Equity [Line Items]
Stock repurchased		1,000,000
Payments for repurchase of preferred stock		$ 100,641,667
Stock exchanged during period shares		1,000,000
Accrued and unpaid dividends		$ 641,667
Series C Preferred Stock [Member]
Temporary Equity [Line Items]
Net proceeds received to derivative liability		2,000,000
Carrying value of preferred stock at issuance		97,000,000
Fair value of derivative liability		2,000,000
Transaction costs		$ 1,000,000
Preferred stock conversion description					The Company will have the right to cause the mandatory conversion of the Series C Preferred Stock into shares of Common Stock (i) at any time after February 26, 2023 if the closing price of the Common Stock has equaled or exceeded 200% of the then-effective conversion price for 45 trading days within a period of 60 consecutive trading days, or (ii) at any time after February 26, 2024 if the closing price of the Common Stock has equaled or exceeded 150% of the then-effective conversion price for 45 trading days within a period of 60 consecutive trading days.
Preferred stock, redemption price per share			$ 100
Preferred stock, right to extend redemption date term		2 years
Series C Preferred Stock [Member] | After February 26, 2023 [Member]
Temporary Equity [Line Items]
Common stock price equal or exceeds preferred stock conversion price percentage					200.00%
Series C Preferred Stock [Member] | After February 26, 2024 [Member]
Temporary Equity [Line Items]
Common stock price equal or exceeds preferred stock conversion price percentage					150.00%
Series C Preferred Stock [Member] | Other Long-Term Liabilities [Member]
Temporary Equity [Line Items]
Fair value of derivative liability					$ 2,000,000
Series C Preferred Stock [Member] | Purchase Agreement [Member]
Temporary Equity [Line Items]
Preferred stock, number of shares issued	250,000	750,000
Preferred stock, liquidation preference per share			$ 100
Preferred stock, number of shares issued		1,000,000
Preferred stock, par value
Gross proceeds from preferred stock	$ 25,000,000	$ 75,000,000
Preferred stock, redemption date			May 28, 2026
Initial conversion price of preferred stock per share of common stock			$ 10
Gross proceeds owed on issuance of preferred stock		$ 100,000,000
Percentage of in-kind dividend payable on preferred stock			5.00%
Series C Preferred Stock [Member] | Dividend and Other Rights [Member]
Temporary Equity [Line Items]
Percentage of in-kind dividend payable on preferred stock			5.00%
Preferred stock, liquidation preference			$ 100
Series C Preferred Stock [Member] | Registration Rights Agreement [Member]
Temporary Equity [Line Items]
Purchase agreement date		Feb. 26, 2021