Note 10 - Stockholders' Equity	12 Months Ended
Dec. 31, 2018
Notes to Financial Statements
Stockholders' Equity Note Disclosure [Text Block]	10 . Stockholders’ Equity Common Stock and Preferred Stock We are authorized to issue 160.0 million shares of our common stock, par value $.0013, and 20.0 million shares of preferred stock, par value $.001. The Board of Directors (the “Board”) has the authority to issue common and preferred shares, in series, with rights and privileges as determined by the Board. Shelf Registration During the first quarter of 2017, we filed a shelf registration statement that permitted: (a) the offering, issuance and sale of up to a maximum aggregate offering price of $250.0 million of our common stock, preferred stock, debt securities, warrants, rights and/or units; and (b) as part of the $250.0 million, the offering, issuance and sale by us of up to a maximum aggregate offering price of $75.0 million of our common stock under our sales agreement with Cantor Fitzgerald & Co. (“Cantor”) in one or more at-the-market (“ATM”) offerings (the “2017 Sales Agreement”). During 2018, we raised $70.0 million, net of underwriting discounts and commissions and offering expenses, in an underwritten public offering of 9.1 million shares of common stock at a public offering price of $8.25 per share, and we sold a total of 3.9 million shares of our common stock in ATM transactions under the sales agreement for net proceeds, after deducting commissions and other transaction costs, of approximately $27.5 million at an average selling price of $7.45 per share. During the fourth quarter of 2017, we sold 0.9 million shares of our common stock in ATM transactions under the sales agreement for net proceeds, after deducting commissions and other transaction costs, of approximately $5.0 million at an average selling price of $6.06 per share. At December 31, 2017, we had 0.3 million shares of our common stock subscribed in ATM transactions under the sales agreement for net proceeds, after deducting commissions and other transaction costs, of approximately $2.1 million at an average selling price of $6.79 per share. Accordingly, we have recorded a subscription receivable of $2.1 million as a reduction of stockholders’ equity in our consolidated balance sheet at December 31, 2017. In October 2018, we filed a new shelf registration statement. The new shelf registration replaced our prior shelf registration statement, pursuant to which no additional securities will be offered or sold. The new shelf registration statement permits: (a) the offering, issuance and sale of up to a maximum aggregate offering price of $250.0 million of our common stock, preferred stock, debt securities, warrants, rights and/or units; and (b) as part of the $250.0 million, the offering, issuance and sale by us of up to a maximum aggregate offering price of $75.0 million of our common stock under our sales agreement with Cantor in one or more ATM offerings. In addition, in October 2018 we entered into a new sales agreement with Cantor, as sales agent, which replaced the 2017 Sales Agreement (the “2018 Sales Agreement”). Pursuant to the 2018 Sales Agreement, we may offer and sell through Cantor, from time to time, shares of our common stock up to an aggregate offering price of $75.0 million. The 2018 Sales Agreement may be terminated by Cantor or us at any time upon ten days’ notice, or by Cantor at any time in certain circumstances, including the occurrence of a material adverse change in our business or financial condition.

. Stockholders’ Equity

Common Stock and Preferred Stock

We are authorized to issue

160.0

million shares of our common stock, par value

$.0013,

and

20.0

million shares of preferred stock, par value

$.001.

The Board of Directors (the “Board”) has the authority to issue common and preferred shares, in series, with rights and privileges as determined by the Board.

Shelf Registration

During the

first

quarter of

2017,

we filed a shelf registration statement that permitted: (a) the offering, issuance and sale of up to a maximum aggregate offering price of

$250.0

million of our common stock, preferred stock, debt securities, warrants, rights and/or units; and (b) as part of the

$250.0

million, the offering, issuance and sale by us of up to a maximum aggregate offering price of

$75.0

million of our common stock under our sales agreement with Cantor Fitzgerald & Co. (“Cantor”) in

one

or more at-the-market (“ATM”) offerings (the

“2017

Sales Agreement”).

During

2018,

we raised

$70.0

million, net of underwriting discounts and commissions and offering expenses, in an underwritten public offering of

9.1

million shares of common stock at a public offering price of

$8.25

per share, and we sold a total of

3.9

million shares of our common stock in ATM transactions under the sales agreement for net proceeds, after deducting commissions and other transaction costs, of approximately

$27.5

million at an average selling price of

$7.45

per share.

During the

fourth

quarter of

2017,

we sold

0.9

million shares of our common stock in ATM transactions under the sales agreement for net proceeds, after deducting commissions and other transaction costs, of approximately

$5.0

million at an average selling price of

$6.06

per share. At

December 31, 2017,

we had

0.3

million shares of our common stock subscribed in ATM transactions under the sales agreement for net proceeds, after deducting commissions and other transaction costs, of approximately

$2.1

million at an average selling price of

$6.79

per share. Accordingly, we have recorded a subscription receivable of

$2.1

million as a reduction of stockholders’ equity in our consolidated balance sheet at

December 31, 2017.

October 2018,

we filed a new shelf registration statement. The new shelf registration replaced our prior shelf registration statement, pursuant to which

additional securities will be offered or sold. The new shelf registration statement permits: (a) the offering, issuance and sale of up to a maximum aggregate offering price of

$250.0

million of our common stock, preferred stock, debt securities, warrants, rights and/or units; and (b) as part of the

$250.0

million, the offering, issuance and sale by us of up to a maximum aggregate offering price of

$75.0

million of our common stock under our sales agreement with Cantor in

one

or more ATM offerings.

In addition, in

October 2018

we entered into a new sales agreement with Cantor, as sales agent, which replaced the

2017

Sales Agreement (the

“2018

Sales Agreement”). Pursuant to the

2018

Sales Agreement, we

may

offer and sell through Cantor, from time to time, shares of our common stock up to an aggregate offering price of

$75.0

million. The

2018

Sales Agreement

may

be terminated by Cantor or us at any time upon

ten

days’ notice, or by Cantor at any time in certain circumstances, including the occurrence of a material adverse change in our business or financial condition.