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Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013
Operating Loss Carryforwards [Line Items] |  |
Increase (decrease) in valuation allowance | $ 7.6 us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount | $ 7.1 us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount
Net operating loss carryforwards expiration year | 2034 |
Internal Revenue Service (IRS) [Member] | Earliest Tax Year [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax year open to examination | 2006 |
Internal Revenue Service (IRS) [Member] | Latest Tax Year [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax year open to examination | 2014 |
Federal [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Net operating loss carryforwards | 77.3 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_DomesticCountryMember |
Federal [Member] | Research [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Research and development credit carryforwards | 1.2 us-gaap_TaxCreditCarryforwardAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_DomesticCountryMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research and development tax credit carryforwards expiration year | 2034 |
State [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Net operating loss carryforwards | 58.1 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |
State [Member] | Research [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Research and development credit carryforwards | $ 0.8 us-gaap_TaxCreditCarryforwardAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research and development tax credit carryforwards expiration year | 2029 |

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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
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- Definition Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=37586315&loc=d3e32123-109318 + Details
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