Stockholders' Equity - Additional Information (Detail) (USD $)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Apr. 04, 2014	Sep. 03, 2014	Dec. 31, 2013
Class Of Stock [Line Items]
Net proceeds from the issuance of common stock	$ 142,541,000
Number of votes per share	One vote per share
Common stock, shares authorized	500,000,000			165,000,000
Common stock, shares issued	81,905,325			53,757,437
Common stock, shares outstanding	81,905,325			53,757,437
Treasury stock, shares	0			0
Series A Convertible Preferred Stock, shares authorized	25,000,000			25,000,000
Series A Convertible Preferred Stock, shares issued	0			19,284,113
Series A Convertible Preferred Stock, shares outstanding	0			19,284,113
Series A Convertible Preferred Stock, liquidation preference				86,200,000
Shares of common stock that would require the Company to repurchase these shares at fair value determined at the redemption date		1,344,236
Redeemable common stock converted, conversion ratio	The put rights that would have required the Company to repurchase the Company’s then outstanding redeemable common stock at fair value (as defined in the stockholders agreement) determined at the redemption date were terminated and the shares converted on a one-for-one basis into an aggregate of 1,344,236 shares of common stock upon the closing of the IPO on April 4, 2014
Redeemable common stock, shares outstanding	0			1,344,236
Redeemable common stock				18,415,000
Annual redemption limit				4,000,000
Common stock
Class Of Stock [Line Items]
Issuance of common stock, net of issuance costs (in shares)	5,250,000
IPO
Class Of Stock [Line Items]
Net proceeds		94,900,000
Initial public offering closing date	Apr. 04, 2014
IPO | Common stock
Class Of Stock [Line Items]
Series A Convertible Preferred Stock, Conversion Description	Upon the closing of the IPO on April 4, 2014, all shares of the Company’s then-outstanding convertible Series A Preferred Stock automatically converted on a one-for-one basis into an aggregate of 19,284,113 shares of common stock.
Number of common shares issued upon conversion of preferred stock		1
Aggregate shares of common stock that convertible Series A Preferred Stock automatically converted into		19,284,113
IPO | Underwriting discounts and commissions
Class Of Stock [Line Items]
Offering expenses		6,500,000
IPO | Other Offering Costs
Class Of Stock [Line Items]
Offering expenses		2,600,000
IPO | Common Class A
Class Of Stock [Line Items]
Issuance of common stock, net of issuance costs (in shares)		4,000,000
Issuance of common stock price per share		$ 26.00
Follow-on Offering
Class Of Stock [Line Items]
Net proceeds from the issuance of common stock			47,600,000
Follow-on Offering | Common stock
Class Of Stock [Line Items]
Issuance of common stock, net of issuance costs (in shares)			1,250,000
Issuance of common stock price per share			$ 40.25
Follow-on Offering | Underwriting discounts and commissions
Class Of Stock [Line Items]
Offering expenses			1,900,000
Follow-on Offering | Other Offering Costs
Class Of Stock [Line Items]
Offering expenses			$ 800,000