Organization, Business and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	May. 12, 2015 USD ($) $ / shares shares	May. 31, 2015 shares	Dec. 31, 2015 USD ($) $ / shares shares	Apr. 30, 2015 shares	Apr. 25, 2015 shares	Dec. 31, 2014 $ / shares shares
Description Of Business [Line Items]
Initial public offering of common stock price per share | $ / shares			$ 0.001			$ 0.001
Net proceeds | $			$ 76,902
Common stock, shares authorized			150,000,000			95,500,000
Preferred stock, shares authorized						75,772,871
Common stock reserved for future issuance			4,766,580			11,053,954
Reverse stock split of company's common stock			On May 5, 2015, we filed an amendment to our amended and restated certificate of incorporation to effect a one-for-7.95413 reverse stock split of our common stock (the Reverse Stock Split). The par value and the authorized shares of the common and convertible preferred stock were not adjusted as a result of the Reverse Stock Split.
Ratio of reverse stock split of company's common stock			7.95413
Pangu BioPharma [Member] | Hong Kong [Member]
Description Of Business [Line Items]
Majority-owned subsidiary percentage			98.00%
2015 ESPP Plan [Member]
Description Of Business [Line Items]
Common stock reserved for future issuance			227,623
Redeemable Convertible Preferred Stock [Member]
Description Of Business [Line Items]
Shares issued upon conversion			(141,654,309)
Preferred stock, shares authorized			7,285,456			75,772,871
Common stock reserved for future issuance						9,238,868
Undesignated Preferred Stock [Member]
Description Of Business [Line Items]
Preferred stock, shares authorized			5,000,000			0
IPO [Member]
Description Of Business [Line Items]
Issuance of common stock through initial public offering, net, Shares	6,164,000
Initial public offering of common stock price per share | $ / shares	$ 14.00
Gross proceeds | $	$ 86,300
Net proceeds | $	75,900
Underwriting and other expenses | $	10,400
Underwriting discounts and commissions | $	6,000
Other offering expenses | $	$ 4,400
Common stock, shares authorized	150,000,000	150,000,000
Preferred stock, shares authorized	7,285,456	7,285,456
IPO [Member] | 2015 Stock Option and Incentive Plan [Member]
Description Of Business [Line Items]
Common stock reserved for future issuance				1,574,566	1,574,566
IPO [Member] | 2015 ESPP Plan [Member]
Description Of Business [Line Items]
Common stock reserved for future issuance				227,623	227,623
IPO [Member] | Redeemable Convertible Preferred Stock [Member]
Description Of Business [Line Items]
Warrants issued upon conversion	206,581	206,581
IPO [Member] | Undesignated Preferred Stock [Member]
Description Of Business [Line Items]
Preferred stock, shares authorized		5,000,000
Preferred stock, shares authorized	5,000,000
Common Stock [Member]
Description Of Business [Line Items]
Issuance of common stock through initial public offering, net, Shares			6,164,000
Shares issued upon conversion			16,279,859
Common Stock [Member] | IPO [Member]
Description Of Business [Line Items]
Shares issued upon conversion	16,279,859	16,279,859
Warrants issued upon conversion	25,970	25,970