Income Taxes (Narrative) (Detail) - USD ($)		3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income tax expense (benefit)				$ (1,302,000)	$ (556,000)
Income tax expense (benefit) related to reduction of existing deferred tax liability					$ (200,000)
United Kingdom enacted tax rate					17.00%	20.00%
Interest and penalties pertaining to income tax examination recognized				$ 0	$ 0
U.S. federal statutory income tax rate				34.00%	34.00%
Additional tax expense from Tax Cuts and Jobs Act				$ 26,000,000
Provisional net tax expense from Tax Cuts and Jobs Act				$ 0
Scenario, Plan [Member]
U.S. federal statutory income tax rate	21.00%
In Process Research and Development [Member]
Impairment of in-process research and development			$ 5,800,000		$ 2,000,000
Income tax expense (benefit) related to reduction of existing deferred tax liability					(400,000)
Maximum [Member]
Income tax examination, years under examination				2016
Minimum [Member]
Income tax examination, years under examination				1998
In Process Research and Development [Member]
Impairment of in-process research and development		$ 0	$ 5,800,000		$ 2,000,000
Domestic Tax Authority [Member]
Net operating loss carryforwards ("NOLs")		198,100,000		$ 198,100,000
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Tax credit carryforward		3,100,000		3,100,000
Unrecognized tax benefits		2,100,000		2,100,000
Foreign Tax Authority [Member]
Net operating loss carryforwards ("NOLs")		9.0		9.0
Tax Year 2017 [Member] | Foreign Tax Authority [Member]
Net operating loss carryforwards ("NOLs")		600,000		600,000
Tax Year 2018 [Member] | Domestic Tax Authority [Member]
Net operating loss carryforwards ("NOLs")		$ 7,300,000		$ 7,300,000