Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 5,485	$ 4,763
Disposal of fixed assets	$ 318	3,400
Reduction in accumulated depreciation due to retirements		2,300
Reduction in property and equipment due to impairment		17
Reduction in accumulated depreciation due to impairment		1
Additional capital lease agreement		884
Accumulated depreciation		1,000
Assets Held under Capital Leases
Property, Plant and Equipment [Line Items]
Disposal of fixed assets		$ 1,700