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Equipment Lease Obligations - Additional Information (Detail) - Equipment - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Capital Leased Assets [Line Items]          
Assets under equipment leases, gross $ 1,484   $ 1,484   $ 2,853
Leased assets, depreciation expense $ 55 $ 73 $ 201 $ 219