Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Taxes And Tax Related [Line Items]
Unrecognized tax benefits, income tax penalties and interest accrued	$ 0	$ 0
Federal [Member]
Income Taxes And Tax Related [Line Items]
Operating tax loss carryforwards, estimated	$ 156,200,000
Operating tax loss carryforwards, estimated expire year	2021
Research and development tax credit carryforward, amount	$ 1,800,000
Research and development tax credit carryforward, amount expire year	2018
Federal alternative minimum tax credit	$ 200,000
State and Local Jurisdiction [Member]
Income Taxes And Tax Related [Line Items]
Operating tax loss carryforwards, estimated	12,600,000
U.K. [Member]
Income Taxes And Tax Related [Line Items]
Operating tax loss carryforwards, estimated	$ 10,900,000