Common Stock	3 Months Ended
Mar. 31, 2019
Stockholders' Equity Note [Abstract]
Stockholders' Equity Note Disclosure [Text Block]	Note 6 – Common and Preferred Stock Shelf Registration In June 2017, the Company filed an automatic shelf registration statement on Form S‑3, registering an unspecified amount at an indeterminant aggregate initial offering price of common stock, preferred stock, depositary shares and warrants. The Company may periodically offer one or more of these securities in amounts, prices and on terms to be announced when and if these securities are offered. The specifics of any future offerings, along with the use of proceeds of any securities offered, will be described in detail in a prospectus supplement, or other offering materials, at the time of any offering. ATM Program In May 2018, the Company entered into a $250.0 million at-the-market equity program (“ATM Program”) through which the Company may, from time to time, sell shares of common stock. In addition to selling shares of common stock, the Company may enter into forward sale agreements through its ATM Program. During the year ended December 31, 2018, the Company issued 3,057,263 shares of common stock under the ATM Program. During the three months ended March 31, 2019, the Company issued an additional 874,268 shares of common stock under this program at an average price of $66.79, realizing gross proceeds of approximately $58.4 million. The Company had approximately $10.4 million remaining under the ATM program as of March 31, 2019. Forward Sale Agreement In September 2018, the Company entered into a follow-on offering of 3,500,000 shares of common stock in connection with a forward sale agreement. As of March 31, 2019, the Company has not received proceeds from the sale of shares of its common stock by the forward purchaser. Selling common stock through the forward sale agreement enabled the Company to set the price of such shares upon pricing the offering (subject to certain adjustments) while delaying the issuance of such shares and the receipt of the net proceeds by the Company. The forward sale agreement is required to be settled no later than September 3, 2019. Preferred Stock During the three months ended March 31, 2019, the Company redesignated and reclassified all 200,000 authorized but unissued shares of the Company’s Series A Junior Participating Preferred Stock as authorized but unissued and unclassified shares of preferred stock, par value $.0001 per share, of the Company without further designation. The number of preferred shares the Company has the authority to issue remains at 4,000,000, all of which are unclassified and undesignated.

Note 6 – Common and Preferred Stock

Shelf Registration

In June 2017, the Company filed an automatic shelf registration statement on Form S‑3, registering an unspecified amount at an indeterminant aggregate initial offering price of common stock, preferred stock, depositary shares and warrants. The Company may periodically offer one or more of these securities in amounts, prices and on terms to be announced when and if these securities are offered. The specifics of any future offerings, along with the use of proceeds of any securities offered, will be described in detail in a prospectus supplement, or other offering materials, at the time of any offering.

ATM Program

In May 2018, the Company entered into a $250.0 million at-the-market equity program (“ATM Program”) through which the Company may, from time to time, sell shares of common stock. In addition to selling shares of common stock, the Company may enter into forward sale agreements through its ATM Program.

During the year ended December 31, 2018, the Company issued 3,057,263 shares of common stock under the ATM Program. During the three months ended March 31, 2019, the Company issued an additional 874,268 shares of common stock under this program at an average price of $66.79, realizing gross proceeds of approximately $58.4 million. The Company had approximately $10.4 million remaining under the ATM program as of March 31, 2019.

Forward Sale Agreement

In September 2018, the Company entered into a follow-on offering of 3,500,000 shares of common stock in connection with a forward sale agreement. As of March 31, 2019, the Company has not received proceeds from the sale of shares of its common stock by the forward purchaser. Selling common stock through the forward sale agreement enabled the Company to set the price of such shares upon pricing the offering (subject to certain adjustments) while delaying the issuance of such shares and the receipt of the net proceeds by the Company. The forward sale agreement is required to be settled no later than September 3, 2019.

Preferred Stock

During the three months ended March 31, 2019, the Company redesignated and reclassified all 200,000 authorized but unissued shares of the Company’s Series A Junior Participating Preferred Stock as authorized but unissued and unclassified shares of preferred stock, par value $.0001 per share, of the Company without further designation. The number of preferred shares the Company has the authority to issue remains at 4,000,000, all of which are unclassified and undesignated.