Financial instruments - Fair Value of Financial Instruments Measured At Fair Value on a Recurring Basis (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments	$ 24,134,541
Investments	8,140,052
Bank loan warrant derivative liabilities	(63,708)	(221,320)
Redemption option on preferred stock		(800,206)
Fair Value of Financial instruments	32,210,885	1,799,074
U.S. Treasury Securities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments	6,138,001
Investments	6,094,143
U.S. government agency securities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments	17,996,540
Investments	2,001,299
Bank Term Deposits [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments		2,820,600
Investments	44,610
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Bank loan warrant derivative liabilities	0	0
Redemption option on preferred stock		0
Fair Value of Financial instruments	32,229,983	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| U.S. Treasury Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments	6,138,001
Investments	6,094,143
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| U.S. government agency securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments	17,996,540
Investments	2,001,299
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Bank Term Deposits [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments		0
Investments	0
Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Bank loan warrant derivative liabilities	0	0
Redemption option on preferred stock		0
Fair Value of Financial instruments	44,610	2,820,600
Other Observable Inputs (Level 2) [Member] \| U.S. Treasury Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments	0
Investments	0
Other Observable Inputs (Level 2) [Member] \| U.S. government agency securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments	0
Investments	0
Other Observable Inputs (Level 2) [Member] \| Bank Term Deposits [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments		2,820,600
Investments	44,610
Significant Un-Observable Inputs (Level 3) [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Bank loan warrant derivative liabilities	(63,708)	(221,320)
Redemption option on preferred stock		(800,206)
Fair Value of Financial instruments	(63,708)	(1,021,526)
Significant Un-Observable Inputs (Level 3) [Member] \| U.S. Treasury Securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments	0
Investments	0
Significant Un-Observable Inputs (Level 3) [Member] \| U.S. government agency securities [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments	0
Investments	0
Significant Un-Observable Inputs (Level 3) [Member] \| Bank Term Deposits [Member] \| Fair Value, Measurements, Recurring [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term investments		0
Investments	$ 0

Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

+ References+ Details

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References+ Details