Stockholders' Equity - Narrative (Details) $ / shares in Units, $ in Millions	1 Months Ended				3 Months Ended	12 Months Ended
	Aug. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($)	Oct. 31, 2017 USD ($) $ / shares shares	May 31, 2016 USD ($)	Sep. 30, 2017 USD ($) shares	Dec. 31, 2019 USD ($) vote $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	May 21, 2019 shares	May 20, 2019 shares
Subsidiary, Sale of Stock [Line Items]
Preferred stock authorized (shares)						10,000,000	10,000,000
Preferred stock par value (in usd per share) | $ / shares						$ 0.001	$ 0.001
Preferred stock issued (shares)						0	0
Preferred stock outstanding (shares)						0	0
Common stock authorized (shares)						100,000,000	50,000,000	100,000,000	50,000,000
Common stock, par value (in usd per share) | $ / shares						$ 0.001	$ 0.001
Number of votes entitled to for each common share held | vote						1
Common stock issued (shares)						45,272,088	42,078,164
Common stock outstanding (shares)						45,272,088	42,078,164
ATM
Subsidiary, Sale of Stock [Line Items]
Gross aggregate proceeds to be received upon stock issuance | $		$ 75.0		$ 25.0
Stock issued (shares)					1,550,880	903,573	740,417
Net proceeds from stock issuance | $					$ 19.4	$ 42.6	$ 30.3
Underwritten Public Offer
Subsidiary, Sale of Stock [Line Items]
Stock issued (shares)	6,000,000		7,700,000
Net proceeds from stock issuance | $	$ 292.9		$ 271.3
Stock offer price (in usd per share) | $ / shares	$ 52.00		$ 37.50