Commitments and Contingencies - Amounts of Assets Under Capitalized Lease Agreements (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Accumulated depreciation	$ (3,006)	$ (2,717)
Net assets under capital leases	760	1,049
Property, Plant and Equipment [Member]
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Assets under capital lease, gross	3,636	3,636
Prepaid Expenses and Other Assets [Member]
Capital Leases, Balance Sheet, Assets by Major Class, Net [Abstract]
Assets under capital lease, gross	$ 130	$ 130