Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Feb. 13, 2018	Dec. 31, 2017	Mar. 31, 2018
Stockholders' Equity (Details) [Line Items]
Preferred Stock, Shares Authorized (in Shares)		5,000,000	5,000,000
Preferred Stock, Par or Stated Value Per Share		$ 0.10	$ 0.10
Preferred Stock, Shares Outstanding (in Shares)		1,221,064	0
Convertible Preferred Stock, Terms of Conversion			At the option of the holder, each share of convertible preferred stock was convertible, one‑for‑one, subject to adjustment for anti‑dilution protection, into shares of common stock. Each share automatically converted into the number of shares of common stock into which the shares were convertible at the then applicable conversion ratio upon: (1) the closing of the sale of the Company’s common stock in a public offering provided the offering price per share was not less than three times the Series C convertible preferred stock original issue price of $33.05196 and the aggregate gross proceeds were not less than $30.0 million, or (2) upon receipt of a written consent of the holders of a majority of the then outstanding shares of convertible preferred stock voting as a single class on an as‑converted basis
Convertible Preferred Stock [Member]
Stockholders' Equity (Details) [Line Items]
Preferred Stock, Shares Authorized (in Shares)		1,662,171
Preferred Stock, Shares Outstanding (in Shares)		1,221,064
Preferred Stock, Voting Rights			The holders of Series A convertible preferred stock, voting as a separate class, were entitled to elect one member of the board of directors. As long as a specified investor held at least one share of Series C convertible preferred stock, the specified investor was able to designate one member of the board of directors, who would have been elected by the holders of Series C convertible preferred stock voting as a separate class. As long as a specified investor held least one share of Series B convertible preferred stock, the specified investor was able to designate one member of the board of directors, who would have been elected by the holders of Series B convertible preferred stock voting as a separate class. The holders of common stock, voting as a separate class, were entitled to elect two members of the board of directors, one of whom was the duly appointed chief executive officer of the Company
Convertible Preferred Stock [Member] | Series C Preferred Stock [Member]
Stockholders' Equity (Details) [Line Items]
Preferred Stock, Shares Authorized (in Shares)		820,088
Preferred Stock, Dividend Rate, Per-Dollar-Amount			$ 2.64416
Preferred Stock, Per Share Amounts of Preferred Dividends in Arrears			33.05196
Dividends, Preferred Stock (in Dollars)	$ 7.3	$ 7.1
Preferred Stock, Dividends Per Share, Declared	$ 12.06	$ 11.74
Preferred Stock, Shares Outstanding (in Shares)		605,103
Shares Issued, Price Per Share			33.05196
Preferred Stock, Liquidation Preference Per Share			$ 33.05196
Convertible Preferred Stock [Member] | Series C Preferred Stock [Member] | Minimum [Member]
Stockholders' Equity (Details) [Line Items]
Preferred Stock, Shares Outstanding (in Shares)			20,134
Proceeds from Issuance of Convertible Preferred Stock (in Dollars)			$ 30.0
Convertible Preferred Stock [Member] | Series B Preferred Stock [Member]
Stockholders' Equity (Details) [Line Items]
Preferred Stock, Shares Authorized (in Shares)		747,095
Preferred Stock, Dividend Rate, Per-Dollar-Amount			$ 2.64416
Preferred Stock, Per Share Amounts of Preferred Dividends in Arrears			33.05196
Dividends, Preferred Stock (in Dollars)	$ 7.6	$ 7.5
Preferred Stock, Dividends Per Share, Declared	$ 15.78	$ 15.56
Preferred Stock, Shares Outstanding (in Shares)	483,387	520,973
Preferred Stock, Liquidation Preference Per Share			$ 33.05196
Convertible Preferred Stock [Member] | Series B Preferred Stock [Member] | Minimum [Member]
Stockholders' Equity (Details) [Line Items]
Preferred Stock, Shares Outstanding (in Shares)			20,134
Convertible Preferred Stock [Member] | Series A Preferred Stock [Member]
Stockholders' Equity (Details) [Line Items]
Preferred Stock, Shares Authorized (in Shares)		94,988
Preferred Stock, Dividend Rate, Per-Dollar-Amount			$ 2.30449
Preferred Stock, Shares Outstanding (in Shares)		94,988
Preferred Stock, Liquidation Preference Per Share			$ 28.80613
Common Stock [Member]
Stockholders' Equity (Details) [Line Items]
Stock Issued During Period, Shares, Acquisitions (in Shares)			3,510,439
Common Stock [Member] | Convertible Preferred Stock [Member] | Series C Preferred Stock [Member]
Stockholders' Equity (Details) [Line Items]
Stock Issued During Period, Shares, Acquisitions (in Shares)	696,028
Common Stock [Member] | Convertible Preferred Stock [Member] | Series C Preferred Stock [Member] | Dividend Paid [Member]
Stockholders' Equity (Details) [Line Items]
Stock Issued During Period, Shares, Acquisitions (in Shares)	253,851
Common Stock [Member] | Convertible Preferred Stock [Member] | Series B Preferred Stock [Member]
Stockholders' Equity (Details) [Line Items]
Stock Issued During Period, Shares, Acquisitions (in Shares)	599,259
Common Stock [Member] | Convertible Preferred Stock [Member] | Series B Preferred Stock [Member] | Dividend Paid [Member]
Stockholders' Equity (Details) [Line Items]
Stock Issued During Period, Shares, Acquisitions (in Shares)	265,340
Common Stock [Member] | Convertible Preferred Stock [Member] | Series A Preferred Stock [Member]
Stockholders' Equity (Details) [Line Items]
Stock Issued During Period, Shares, Acquisitions (in Shares)	104,065