Fair Value Measurements - Fair Value of Assets and Liabilities (Details) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Liabilities:
Derivative financial instruments—warrants	$ 279,434	$ 834,940
Estimate of Fair Value Measurement
Assets:
Available-for-sale Securities	18,619,712	23,978,022
Estimate of Fair Value Measurement \| Corporate debt securities
Assets:
Available-for-sale Securities	3,743,945	14,160,686
Estimate of Fair Value Measurement \| Commercial paper
Assets:
Available-for-sale Securities	6,273,140	1,195,444
Estimate of Fair Value Measurement \| U.S. treasury securities
Assets:
Available-for-sale Securities	8,602,627	8,621,892
Recurring basis \| Corporate debt securities
Assets:
Available-for-sale Securities	3,743,945	14,160,686
Recurring basis \| Commercial paper
Assets:
Available-for-sale Securities	7,272,879	2,393,948
Recurring basis \| U.S. treasury securities
Assets:
Available-for-sale Securities	8,602,627	8,621,892
Recurring basis \| Estimate of Fair Value Measurement
Assets:
Money market fund	8,707,706	12,095,620
Total Assets	28,327,157	37,272,146
Liabilities:
Derivative financial instruments—warrants	279,434	834,940
Total Liabilities	279,434	834,940
Recurring basis \| Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1)
Assets:
Money market fund	8,707,706	12,095,620
Total Assets	8,707,706	12,095,620
Liabilities:
Derivative financial instruments—warrants	0	0
Total Liabilities	0	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) \| Corporate debt securities
Assets:
Available-for-sale Securities	0	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) \| Commercial paper
Assets:
Available-for-sale Securities	0	0
Recurring basis \| Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1) \| U.S. treasury securities
Assets:
Available-for-sale Securities	0	0
Recurring basis \| Significant Other Observable Inputs (Level 2)
Assets:
Money market fund	0	0
Total Assets	19,619,451	25,176,526
Liabilities:
Derivative financial instruments—warrants	0	0
Total Liabilities	0	0
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Corporate debt securities
Assets:
Available-for-sale Securities	3,743,945	14,160,686
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Commercial paper
Assets:
Available-for-sale Securities	7,272,879	2,393,948
Recurring basis \| Significant Other Observable Inputs (Level 2) \| Commercial paper \| Cash and Cash Equivalents
Assets:
Available-for-sale Securities	999,739	1,198,504
Recurring basis \| Significant Other Observable Inputs (Level 2) \| U.S. treasury securities
Assets:
Available-for-sale Securities	8,602,627	8,621,892
Recurring basis \| Significant Unobservable Inputs (Level 3)
Assets:
Money market fund	0	0
Total Assets	0	0
Liabilities:
Derivative financial instruments—warrants		834,940
Total Liabilities	279,434	834,940
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Corporate debt securities
Assets:
Available-for-sale Securities	0	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| Commercial paper
Assets:
Available-for-sale Securities	0	0
Recurring basis \| Significant Unobservable Inputs (Level 3) \| U.S. treasury securities
Assets:
Available-for-sale Securities	$ 0	$ 0

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

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-Name Accounting Standards Codification
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Fair value of financial and nonfinancial obligations.

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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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