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.