Nature of Organization and Operations - Additional Information (Details) $ / shares in Units, $ in Thousands			1 Months Ended	6 Months Ended
	Mar. 25, 2014 USD ($) $ / shares shares	Mar. 06, 2014	Apr. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares
Nature Of Organization And Operations [Line Items]
Common stock, shares authorized	175,000,000			175,000,000	175,000,000
Preferred stock, shares authorized	25,000,000			25,000,000	25,000,000
Cash and cash equivalents and available for sale securities | $				$ 152,789	$ 108,918
Stock split, conversion ratio		1.75
Entity incorporation date				Feb. 27, 2007
IPO
Nature Of Organization And Operations [Line Items]
Sale of stock, price per share | $ / shares	$ 17.00
Proceeds from issuance of initial public offering | $	$ 104,400
Convertible redeemable preferred stock converted into common stock	12,115,183
Follow-on public offering
Nature Of Organization And Operations [Line Items]
Sale of stock, price per share | $ / shares			$ 8.25
Proceeds from issuance of initial public offering | $			$ 64,600
Common Stock | IPO
Nature Of Organization And Operations [Line Items]
Issuance of common stock, shares	6,762,000
Common Stock | Overallotment option granted to underwriters
Nature Of Organization And Operations [Line Items]
Issuance of common stock, shares	879,647		1,090,909
Common Stock | Follow-on public offering
Nature Of Organization And Operations [Line Items]
Issuance of common stock, shares			8,363,636