Net Loss per Share - Summary of Computation of Basic and Diluted Net Loss Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended	73 Months Ended
Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Earnings Per Share [Abstract]
Net loss attributable to common stockholders - basic and diluted	$ (15,653)	$ (13,834)	$ (8,600)	$ (44,985)	$ (5,814)	$ (5,009)	$ (3,655)	$ (4,019)	$ (83,072)	$ (18,497)	$ (13,217)	$ (136,818)
Weighted-average shares outstanding									18,921,533	450,061	130,718
Less: weighted average shares subject to repurchase										(61)	(15,499)
Weighted-average shares used to compute basic and diluted net loss per share	24,215,018	24,194,808	24,194,808	2,788,087	1,257,250	250,745	147,713	132,969	18,921,533	450,000	115,219
Basic and diluted net loss per common share	$ (0.65)us-gaap_EarningsPerShareBasicAndDiluted	$ (0.57)us-gaap_EarningsPerShareBasicAndDiluted	$ (0.36)us-gaap_EarningsPerShareBasicAndDiluted	$ (16.13)us-gaap_EarningsPerShareBasicAndDiluted	$ (4.62)us-gaap_EarningsPerShareBasicAndDiluted	$ (19.98)us-gaap_EarningsPerShareBasicAndDiluted	$ (24.74)us-gaap_EarningsPerShareBasicAndDiluted	$ (30.23)us-gaap_EarningsPerShareBasicAndDiluted	$ (4.39)us-gaap_EarningsPerShareBasicAndDiluted	$ (41.10)us-gaap_EarningsPerShareBasicAndDiluted	$ (114.71)us-gaap_EarningsPerShareBasicAndDiluted

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The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

No definition available.

+ Details

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- Definition

Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1377-109256

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- Definition

Average number of shares or units issued and outstanding that are used in calculating basic and diluted earnings per share (EPS).

+ References

No definition available.

+ Details

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- Definition

Number of shares of common stock subject to repurchase or cancellation determined by relating the portion of time within a reporting period that these shares have been outstanding to the total time in that period. Common stock subject to repurchase are outstanding common shares that are contingently returnable (that is, subject to recall).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 45

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e2646-109256

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- Definition

This element represents the weighted average total number of shares issued throughout the period including the first (beginning balance outstanding) and last (ending balance outstanding) day of the period before considering any reductions (for instance, shares held in treasury) to arrive at the weighted average number of shares outstanding. Weighted average relates to the portion of time within a reporting period that common shares have been issued and outstanding to the total time in that period. Such concept is used in determining the weighted average number of shares outstanding for purposes of calculating earnings per share (basic).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 45

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e2646-109256

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 45

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1448-109256

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