Summary of Significant Accounting Policies - Follow-On Public Offering (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		2 Months Ended	9 Months Ended
	May. 31, 2015	Apr. 30, 2015	May. 31, 2015	Sep. 30, 2015	Sep. 30, 2014
Class of Stock [Line Items]
Net proceeds from stock issuance			$ 75,400	$ 75,359	$ 57,807
Offering costs			$ 5,400
Common Stock [Member]
Class of Stock [Line Items]
Additional shares of common stock issued (in shares)	47,409	3,000,000
Share price (in dollars per share)	$ 26.50	$ 26.50	$ 26.50