Stockholder's Equity - Narrative (Details) - USD ($)				1 Months Ended	9 Months Ended		23 Months Ended
	Sep. 15, 2016	Nov. 03, 2014	Sep. 30, 2014	Oct. 31, 2013	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016
Class of Stock [Line Items]
Common stock initial public offering (shares)				7,728,000
Net proceeds from initial public offering				$ 68,300,000
Proceeds from sale of common stock					$ 168,479,000	$ 47,100,000
Cantor Fitzgerald and Co. | Common stock
Class of Stock [Line Items]
Proceeds from sale of common stock	$ 71,000,000
Shares issued under shelf registration	2,542,373
Shelf registration, price per share issued under underwriting agreement	$ 29.50
Underwriting discounts, fees and expenses under sale of stock	$ 4,000,000
RBC Capital Markets LLC and Cantor Fitzgerald and Co | Common stock
Class of Stock [Line Items]
Shelf registration statement, aggregate dollar amount					$ 96,200,000
Common stock issued and sold under sales agreement (shares)					4,179,156		5,933,712
Proceeds from sale of common stock							$ 146,600,000
Sale of stock, commissions, percentage of gross sales (up to) (as a percentage)							3.00%
Convertible notes
Class of Stock [Line Items]
Proceeds from issuance of convertible notes, net of discounts			$ 122,900,000
Maximum
Class of Stock [Line Items]
Shelf registration statement, aggregate dollar amount		$ 150,000,000.0
IPO
Class of Stock [Line Items]
Public offering price of the shares sold (in USD per share)				$ 10.00