Stockholders' Equity (Details) - USD ($) $ in Millions	1 Months Ended		9 Months Ended
	May 31, 2016	Mar. 31, 2015	Sep. 30, 2016
Cantor Fitzgerald & Co. Agreement
Stockholders' Equity
Common stock issued (in shares)			2,395,949
Net proceeds from sale of stock			$ 10.7
Maximum aggregate offering price of common stock	$ 60.0
Fixed commission rate	3.00%
Aggregate gross offering price available			$ 48.8
Underwritten Public Offering
Stockholders' Equity
Common stock issued (in shares)		8,337,500
Net proceeds from sale of stock		$ 188.8