Property and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 6,400,000	$ 5,000,000	$ 4,700,000
Loss on write-offs of fully deprecated property and equipment	0
Deprecated property and equipment, value	$ 17,100,000
Deprecated property and equipment, basis of valuation	Cost Basis
Property and equipment, accumulated depreciation	$ 18,022,000	$ 30,346,000
Corvallis Plan [Member]
Property, Plant and Equipment [Line Items]
Accelerated depreciation	$ 800,000