Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Significant Accounting Policies [Line Items]
Maturity of highly liquid investments	Three months or less
Maturity of certificates of deposit, commercial paper, corporate notes and corporate bonds	More than three months
Available-for-sale investment securities	$ 177,903,693		$ 68,320,672
Carrying value of cash held in money market funds	16,800,000		8,500,000
Allowance recorded	$ 0		0
Assumed expected dividend rate	0.00%	0.00%
Excess tax benefits for tax deductions	$ 0	$ 0
Significant Unobservable Inputs (Level 3) [Member]
Significant Accounting Policies [Line Items]
Assets measured using quoted prices	0		0
Liabilities measured using quoted prices	0		0
Contractual Maturity Dates More Than One Year and Less Than Two Years [Member]
Significant Accounting Policies [Line Items]
Available-for-sale investment securities	$ 78,900,000		$ 31,800,000
Minimum [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	3 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	5 years

Available For Sale Securities Maturity Period

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Maturity period of liquid investments to be considered as cash equivalents.

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Significant accounting policies.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

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Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

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-Publisher FASB

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Amount of cash outflow for realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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- Definition

Fair value of financial and nonfinancial obligations.

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- Definition

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (f)(2)(iii)

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