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Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Income Taxes [Line Items] |  |  |
Deferred state income tax expense (benefit) | $ 4,145 | $ (500) | $ 3,573
Deferred tax assets, operating loss carryforwards, federal | 9,900 |  |
Deferred tax assets, operating loss carryforwards, state | 2,100 |  |
Net Operating Loss Carryforwards | 23,921 | 10,500 |
Tax Credit Carryforwards | 3,365 | $ 2,677 |
New Hampshire Department of Revenue (Business Enterprise Tax) |  |  |
Income Taxes [Line Items] |  |  |
Deferred state income tax expense (benefit) | $ (700) |  |
Internal Revenue Service (IRS) |  |  |
Income Taxes [Line Items] |  |  |
NOL carryforward assets expiration date | 2029 |  |
Federal, Maine, Massachusetts, and New Hampshire Tax Authorities |  |  |
Income Taxes [Line Items] |  |  |
Tax examination description | The Company remains subject to examination by Federal, Maine, Massachusetts, and New Hampshire tax authorities for the tax periods ended December 31, 2013; December 31, 2014; and December 31, 2015. |  |

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