Note 9 - Redeemable, Convertible Series A Preferred Stock (Details Textual)			12 Months Ended
	Nov. 15, 2016 USD ($) $ / shares shares	Nov. 14, 2016 Member Director $ / shares	Dec. 31, 2017 USD ($) Director	Dec. 31, 2016 USD ($)
Temporary Equity [Line Items]
Net proceeds from the issuance of preferred stock				$ 198,000,000
Expected number of members to nominate on conversion basis | Member		2
Series A Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Net proceeds from the issuance of preferred stock	$ 198,000,000
Stock issuance costs	$ 2,000,000
Series A Redeemable Preferred Stock [Member] | Mandatorily Redeemable [Member]
Temporary Equity [Line Items]
Preferred stock, redemption date			Nov. 15, 2021
Series A Redeemable Preferred Stock [Member] | Purchase Agreement [Member]
Temporary Equity [Line Items]
Preferred stock, number of shares issued | shares	2,000,000
Percentage of cash dividend payable on preferred stock	5.50%
Gross proceeds from issuance of shares	$ 200,000,000
Preferred stock, liquidation preference per share | $ / shares	$ 100
Purchase agreement date			Nov. 07, 2016
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Percentage of cash dividend payable on preferred stock		5.50%
Preferred stock, redemption date			Nov. 15, 2021
Preferred stock, liquidation preference | $ / shares		$ 100
Number of additional directors to elect if dividends in arrears | Director		2
Number of directors nominated by purchasers | Director			2
Common stock price equal or exceeds preferred stock conversion price percentage			125.00%
Preferred stock conversion description			The Company will have the right to convert Series A Preferred Stock into Common Stock at any time after the second anniversary of the initial issuance, if the closing price of the Common Stock has equaled or exceeded 125 percent of the then-effective conversion price for 45 trading days within a period of 60 consecutive trading days, with the last trading day of such 60 day period ending on the trading day immediately preceding the business day on which the Company issues a press release announcing the mandatory conversion.
Net proceeds received to derivative liability			$ 43,000,000
Fair value of derivative liability				43,000,000
Carrying value of Series A preferred stock at issuance	$ 155,000,000
Gross proceeds from preferred stock	200,000,000
Transaction costs	$ 2,000,000
Preferred stock, redemption price per share | $ / shares	$ 100
Series A Preferred Stock [Member] | Other Long-Term Assets [Member]
Temporary Equity [Line Items]
Fair value of derivative asset			$ 4,000,000
Series A Preferred Stock [Member] | Other Noncurrent Liabilities [Member]
Temporary Equity [Line Items]
Fair value of derivative liability				$ 43,000,000
Series A Preferred Stock [Member] | Purchase Agreement [Member]
Temporary Equity [Line Items]
Initial conversion rate of preferred stock to common stock | shares	5.7471
Initial conversion price of preferred stock per share of common stock | $ / shares	$ 17.40
Series A Preferred Stock [Member] | Registration Rights Agreement [Member]
Temporary Equity [Line Items]
Purchase agreement date			Nov. 15, 2016
Series A Preferred Stock [Member] | Registration Rights Agreement [Member] | Minimum [Member]
Temporary Equity [Line Items]
Aggregate market value of preferred stock	$ 75,000,000