Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Jan. 31, 2019	Dec. 31, 2018
Common Stock [Member]
Class of Stock [Line Items]
Shares issued upon conversion (in share)				782,031
Series F Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		0		2,737	2,737
Underwriting Agreement [Member]
Class of Stock [Line Items]
Number of shares of common stock issued (in shares)	3,910,000
Price per share (usd per share)	$ 29.50		$ 29.50
Proceeds from sale of stock	$ 115.3
Proceeds, net of underwriting commissions	109.8
Sale of stock issuance costs	$ 5.5
Common Stock [Member]
Class of Stock [Line Items]
Stock issued during period (in shares)	43,056	782,000	3,910,000
Warrants exercised during period (in shares)	83,013
Warrants outstanding (in shares)		10,000