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Summary of Significant Accounting Policies - Additional Information (Detail) | 1 Months Ended | 3 Months Ended | 12 Months Ended | 14 Months Ended |
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Aug. 31, 2015 shares | Apr. 30, 2015 $ / shares shares | Feb. 28, 2015 USD ($) | Jul. 31, 2014 $ / shares shares | Oct. 31, 2013 $ / shares shares | Apr. 30, 2013 USD ($) | Dec. 31, 2011 $ / shares shares | Dec. 31, 2014 USD ($) shares | Dec. 31, 2015 USD ($) Segment Employees $ / shares shares | Dec. 31, 2014 USD ($) shares | Nov. 30, 2014 USD ($) | Dec. 31, 2013 shares | Dec. 31, 2012 shares | Dec. 31, 2011 $ / shares shares | Aug. 31, 2014 USD ($) | Apr. 01, 2009 USD ($)
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of segments | Segment |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Accumulated deficit |  |  |  |  |  |  |  | $ (420,271,608) | $ (456,686,634) | $ (420,271,608) |  |  |  |  |  |
Maturity period for market accounts, money market funds and investments |  |  |  |  |  |  |  |  | 90 days |  |  |  |  |  |  |
Impairment of goodwill |  |  |  |  |  |  |  |  |  | 1,910,062 | $ 1,910,062 |  |  |  |  |
Other intangible assets, net |  |  |  |  |  |  |  | 356,889 | $ 45,816 | 356,889 |  |  |  |  |  |
Impairment amount of intangible asset |  |  |  |  |  |  |  | 530,000 | 239,000 | 530,000 |  |  |  |  |  |
Value of patent |  |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |
Fair value of certain lab equipment |  |  |  |  |  |  |  |  | $ 0 | 0 |  |  |  |  |  |
Term of loan |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |
Annual interest rate on loan |  |  |  |  |  |  |  |  | 6.00% |  |  |  |  |  |  |
Final fee payment at the end of loan term |  |  |  |  |  |  |  |  | $ 1,000,000 |  |  |  |  |  |  |
Exercise price of warrants | $ / shares |  | $ 0.85 |  | $ 2.17 | $ 1.80 |  |  |  |  |  |  |  |  |  |  |
Initial carrying amount assigned to loan, net of discount |  |  |  |  |  |  |  |  | 9,512,000 |  |  |  |  |  |  |
Fair value allocated to warrant |  |  |  |  |  |  |  |  | 388,000 |  |  |  |  |  |  |
Note issuance costs |  |  |  |  |  |  |  |  | $ 117,000 |  |  |  |  |  |  |
Deferred financing costs, discount and accretion percentage |  |  |  |  |  |  |  |  | 9.00% |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants | shares |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Number of shares issued upon Series B warrants exercise | shares |  | 35,715,000 |  | 11,299,435 | 12,845,500 |  |  |  |  |  |  |  |  |  |  |
Fair value of warrant liability |  |  |  |  |  |  |  | 1,684,551 | $ 770,964 | 1,684,551 |  |  |  |  |  |
Accrued expenses and accrued liabilities |  |  |  |  |  |  |  | $ 4,869,710 | $ 5,731,596 | $ 4,869,710 |  |  |  |  |  |
Employee Severance [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of employees eliminated | Employees |  |  |  |  |  |  |  |  | 17 |  |  |  |  |  |  |
Percentage of employees eliminated |  |  |  |  |  |  |  |  | 25.00% |  |  |  |  |  |  |
Severance and related expenses |  |  |  |  |  |  |  |  | $ 392,000 |  |  |  |  |  |  |
Accrued expenses and accrued liabilities |  |  |  |  |  |  |  |  | 392,000 |  |  |  |  |  |  |
Silicon Valley Bank Loan Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from loan |  |  |  |  |  | $ 9,900,000 |  |  |  |  |  |  |  |  |  |
Cash discount |  |  |  |  |  | 100,000 |  |  | $ 100,000 |  |  |  |  |  |  |
Term of loan |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |
Annual interest rate on loan |  |  |  |  |  |  |  |  | 6.00% |  |  |  |  |  |  |
Final fee payment at the end of loan term |  |  |  |  |  |  |  |  | $ 1,000,000 |  |  |  |  |  |  |
Initial carrying amount assigned to loan, net of discount |  |  |  |  |  |  |  |  | 9,512,000 |  |  |  |  |  |  |
Fair value allocated to warrant |  |  |  |  |  |  |  |  | 388,000 |  |  |  |  |  |  |
Note issuance costs |  |  |  |  |  |  |  |  | $ 117,000 |  |  |  |  |  |  |
Deferred financing costs, discount and accretion percentage |  |  |  |  |  |  |  |  | 9.00% |  |  |  |  |  |  |
Minimum cash proceeds from investors required to release pledged restricted money market account |  |  |  |  |  |  |  |  | $ 18,000,000 |  |  |  |  |  |  |
Silicon Valley Bank Loan Agreement [Member] | Restricted Money Market Account [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, collateral amount |  |  |  |  |  |  |  |  | 2,422,500 |  |  |  |  |  |  |
CIRM [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Approval of fund by California Institute for Regenerative Medicine (CIRM) |  |  |  |  |  | 19,300,000 |  |  |  |  |  |  |  |  |  |
Aggregate proceeds from disbursement of the loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 9,600,000 |
Forgiveness of loan principal |  |  |  |  |  |  |  |  | 8,917,000 |  |  |  |  |  |  |
Accrued interest forgiven |  |  |  |  |  |  |  |  | 243,000 |  |  |  |  |  |  |
Repayment of aggregate loan proceeds received |  |  | $ 679,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Silicon Valley Bank [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from loan |  |  |  |  |  | 9,900,000 |  |  |  |  |  |  |  |  |  |
Cash discount |  |  |  |  |  | $ 100,000 |  |  |  |  |  |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities callable by warrants | shares |  |  |  |  |  |  |  | 1,180,015 |  | 1,180,015 |  |  |  |  |  |
Number of securities callable by each warrant or right warrants | shares |  | 0.75 |  | 0.85 | 0.5 |  |  |  |  |  |  |  |  |  |  |
Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value of warrant liability |  |  |  |  |  |  |  |  | $ 771,000 |  |  |  |  |  |  |
Marketable debt securities, current [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investments with maturities |  |  |  |  |  |  |  |  | 365 days or less |  |  |  |  |  |  |
Marketable securities, non-current [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investments with maturities |  |  |  |  |  |  |  |  | Greater than 365 days |  |  |  |  |  |  |
Stem Cell Sciences Holdings Ltd [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5,135,000
Percentage of purchase price allocated to goodwill |  |  |  |  |  |  |  | 42.00% |  |  |  |  |  |  |  |
Impairment of goodwill |  |  |  |  |  |  |  | $ 1,910,000 |  |  |  |  |  |  |  |
Series A Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants | shares |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Series A Warrants [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price of warrants | $ / shares |  | $ 0.70 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Silicon Valley Bank Loan Agreement Warrant [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term of warrant |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |  |
Exercise price of warrants | $ / shares |  |  |  |  |  |  |  |  | $ 1.7034 |  |  |  |  |  |  |
Warrant expiration period |  |  |  |  |  |  |  |  | April 2023 |  |  |  |  |  |  |
Silicon Valley Bank Loan Agreement Warrant [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities callable by warrants | shares |  |  |  |  |  |  |  |  | 293,531 |  |  |  |  |  |  |
December 2011 Financing [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of securities callable by each warrant or right warrants | shares |  |  |  |  |  |  | 1 |  | 1 |  |  |  |  | 1 |  |
Number of shares issued upon Series B warrants exercise | shares |  |  |  |  |  |  |  |  |  |  |  |  | 2,700,000 |  |  |
December 2011 Financing [Member] | Series A Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term of warrant |  |  |  |  |  |  | 5 years |  |  |  |  |  |  |  |  |
Number of securities callable by warrants | shares |  |  |  |  |  |  | 8,000,000 |  |  |  |  |  |  | 8,000,000 |  |
Number of securities callable by each warrant or right warrants | shares |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Number of warrants exercised | shares |  |  |  |  |  |  |  |  |  | 1,180,015 |  | 384,534 | 2,198,571 |  |  |
Number of warrants issued upon Series B warrants exercise | shares |  |  |  |  |  |  |  |  |  |  |  |  | 2,700,000 |  |  |
December 2011 Financing [Member] | Series A Warrants [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price of warrants | $ / shares |  |  |  |  |  |  | $ 1.40 |  |  |  |  |  |  | $ 1.40 |  |
Number of shares issued upon Series B warrants exercise | shares |  |  |  |  |  |  |  |  |  | 1,180,015 |  | 384,534 | 2,198,571 |  |  |
December 2011 Financing [Member] | Series B Warrants [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term of warrant |  |  |  |  |  |  | 90 days |  |  |  |  |  |  | 90 days |  |
Number of securities callable by warrants | shares |  |  |  |  |  |  | 8,000,000 |  |  |  |  |  |  | 8,000,000 |  |
Exercise price of warrants | $ / shares |  |  |  |  |  |  | $ 1.25 |  |  |  |  |  |  | $ 1.25 |  |
Number of warrants exercised | shares |  |  |  |  |  |  |  |  |  |  |  |  | 2,700,000 |  |  |
Number of warrants expired | shares |  |  |  |  |  |  |  |  | 5,300,000 |  |  |  | 5,300,000 |  |  |
April 2015 Financing [Member] | Series A Warrants [Member] | Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Exercise price of warrants | $ / shares |  | $ 0.70 |  |  |  |  |  |  | $ 0.52 |  |  |  |  |  |  |
July 2014 Financing [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Class of Warrant or Right [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of warrants expired | shares | 9,604,520 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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