Subsequent Events	12 Months Ended
Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On February 19, 2019 and March 1, 2019, the Company completed a private placement of $78.5 million aggregate principal amount of its 6.50% convertible senior notes due 2024 (the “Notes”). The notes were sold in a private offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended. The Company estimates that the net proceeds from the offering were approximately $75.8 million, after deducting the initial purchasers' discount and estimated offering expenses payable by the Company. The notes will be senior unsecured obligations of the Company and will accrue interest payable in cash semi-annually in arrears at a rate of 6.50% per annum. The notes will mature on March 1, 2024, unless earlier converted, redeemed or repurchased. Prior to the close of business on the business day immediately preceding November 1, 2023, the notes will be convertible at the option of the holders only upon the satisfaction of certain circumstances. Thereafter, the notes will be convertible at the option of the holders at any time until the close of business on the scheduled trading day immediately before the maturity date. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election. The initial conversion rate will be 185.8045 shares per $1,000 principal amount of notes (equivalent to an initial conversion price of approximately $5.38 per share), subject to adjustment upon the occurrence of specified events. The Company may not redeem the notes prior to March 1, 2022. On or after March 1, 2022, the Company may redeem all, or any portion, of the notes for cash if the last reported sale price per share of the Company's common stock exceeds 130% of the conversion price on (i) each of at least 20 trading days (whether or not consecutive) during the 30 consecutive trading days ending on, and including, the trading day immediately before the Company sends the related redemption notice; and (ii) the trading day immediately before the date the Company sends such redemption notice. The redemption price will be equal to 100% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. On February 21, 2019, the Company announced the completion of a spin-out of its previously wholly-owned subsidiary Geneos Therapeutics, Inc. (“Geneos”). On February 21, 2019, Geneos completed the initial closing of a preferred stock financing with outside investors. The Company participated in the preferred stock financing, which was led by an outside investor. The terms of the stock purchase agreement include commitments for additional investments by the Company and the other investors upon the occurrence of a specified regulatory event, as well as an option on the part of the Company and the other investors to purchase additional preferred stock of Geneos upon the achievement of a specified milestone. Following the initial closing of the financing transaction, the Company continues to hold a majority of the outstanding equity, on an as-converted to common stock basis, of Geneos. The Company’s ownership percentage of Geneos would decrease in the event of additional purchases of preferred stock of Geneos by the other investors under the terms of the stock purchase agreement.

Subsequent Events

On February 19, 2019 and March 1, 2019, the Company completed a private placement of $78.5 million aggregate principal amount of its 6.50% convertible senior notes due 2024 (the “Notes”). The notes were sold in a private offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended. The Company estimates that the net proceeds from the offering were approximately $75.8 million, after deducting the initial purchasers' discount and estimated offering expenses payable by the Company.

The notes will be senior unsecured obligations of the Company and will accrue interest payable in cash semi-annually in arrears at a rate of 6.50% per annum. The notes will mature on March 1, 2024, unless earlier converted, redeemed or repurchased. Prior to the close of business on the business day immediately preceding November 1, 2023, the notes will be convertible at the option of the holders only upon the satisfaction of certain circumstances. Thereafter, the notes will be convertible at the option of the holders at any time until the close of business on the scheduled trading day immediately before the maturity date. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election. The initial conversion rate will be 185.8045 shares per $1,000 principal amount of notes (equivalent to an initial conversion price of approximately $5.38 per share), subject to adjustment upon the occurrence of specified events.

The Company may not redeem the notes prior to March 1, 2022. On or after March 1, 2022, the Company may redeem all, or any portion, of the notes for cash if the last reported sale price per share of the Company's common stock exceeds 130% of the conversion price on (i) each of at least 20 trading days (whether or not consecutive) during the 30 consecutive trading days ending on, and including, the trading day immediately before the Company sends the related redemption notice; and (ii) the trading day immediately before the date the Company sends such redemption notice. The redemption price will be equal to 100% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date.

On February 21, 2019, the Company announced the completion of a spin-out of its previously wholly-owned subsidiary Geneos Therapeutics, Inc. (“Geneos”). On February 21, 2019, Geneos completed the initial closing of a preferred stock financing with outside investors. The Company participated in the preferred stock financing, which was led by an outside investor. The terms of the stock purchase agreement include commitments for additional investments by the Company and the other investors upon the occurrence of a specified regulatory event, as well as an option on the part of the Company and the other investors to purchase additional preferred stock of Geneos upon the achievement of a specified milestone. Following the initial closing of the financing transaction, the Company continues to hold a majority of the outstanding equity, on an as-converted to common stock basis, of Geneos. The Company’s ownership percentage of Geneos would decrease in the event of additional purchases of preferred stock of Geneos by the other investors under the terms of the stock purchase agreement.