Summary of Significant Accounting Policies - Estimated Useful Lives of Property Plant and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 6,675	$ 7,657
Less: accumulated depreciation	(4,672)	(4,541)
Property Plant And Equipment, Net	2,003	3,116
Building and Building Improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	2,162	2,700
Property and Equipment
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 4,513	$ 4,957
Minimum | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment, useful life	10 years
Minimum | Property and Equipment
Property, Plant and Equipment [Line Items]
Property plant and equipment, useful life	2 years
Maximum | Building and Building Improvements
Property, Plant and Equipment [Line Items]
Property plant and equipment, useful life	40 years
Maximum | Property and Equipment
Property, Plant and Equipment [Line Items]
Property plant and equipment, useful life	10 years