Amount of decrease in additional paid in capital (APIC) resulting from direct costs associated with issuing stock. Includes, but is not limited to, legal and accounting fees and direct costs associated with stock issues under a shelf registration.

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Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

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The number of new shares issued in the conversion of stock in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

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The cash inflow associated with the amount received from entity's first offering of stock to the public.

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-Glossary Financing Activities

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The cash inflow from the additional capital contribution to the entity.

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Amount per share or per unit of equity securities issued by non-development stage entity.

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Number of new stock issued during the period.

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Organization and Reorganization - Additional Information (Detail) (USD $)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Apr. 04, 2014	Sep. 03, 2014
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Net proceeds from the issuance of common stock	$ 142,541,000
Common stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock	5,250,000
IPO
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Net proceeds		94,900,000
IPO \| Common stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of Series A preferred stock shares converted into common stock		19,284,113
IPO \| Selling stockholders \| Common stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock		3,405,614
Number of options to purchase shares of common stock offered to underwriters		1,110,842
IPO \| Underwriting discounts and commissions
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Offering expenses		6,500,000
IPO \| Other Offering Costs
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Offering expenses		2,600,000
IPO \| Common Class A
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock		4,000,000
Issuance of common stock price per share		$ 26.00
Follow-on Offering
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Net proceeds from the issuance of common stock			47,600,000
Follow-on Offering \| Common stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock			1,250,000
Issuance of common stock price per share			$ 40.25
Follow-on Offering \| Selling stockholders \| Common stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Issuance of common stock			9,218,198
Number of options to purchase shares of common stock offered to underwriters			1,570,229
Follow-on Offering \| Underwriting discounts and commissions
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Offering expenses			1,900,000
Follow-on Offering \| Other Offering Costs
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Offering expenses			$ 800,000