Note 8 - Redeemable, Convertible Series A Preferred Stock (Details Textual)		3 Months Ended
	Nov. 15, 2016 USD ($) Member Director $ / shares shares	Mar. 31, 2019 USD ($) Director $ / shares shares	Dec. 31, 2018 USD ($)
Temporary Equity [Line Items]
Expected number of members to nominate on conversion basis | Member	2
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%
Net proceeds received to 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
Fair value of derivative liability	43,000,000
Transaction costs	$ 2,000,000
Preferred stock, redemption date	Nov. 15, 2021
Number of additional directors to elect if dividends in arrears | Director	2
Number of directors nominated by purchasers | Director		2
Number of shares redeemed | shares		0
Preferred stock, redemption price per share | $ / shares		$ 100
Preferred stock conversion description		As of March 31, 2019, the Series A Preferred Stock has not been converted and none of the antidilution provisions have been triggered. Any shares of Series A Preferred Stock not converted prior to the fifth anniversary of the initial issuance of the Series A Preferred Stock are required to be redeemed at $100 per share plus the amount of accrued and unpaid dividends
Dividend Declared [Member]
Temporary Equity [Line Items]
Dividends		$ 0	$ 0