Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Summary of Property Plant and Equipment and Rental Equipment with Associated Accumulated Depreciation (Details)

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Summary of Significant Accounting Policies - Summary of Property Plant and Equipment and Rental Equipment with Associated Accumulated Depreciation (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Property Plant And Equipment [Line Items]    
Property and equipment $ 64,634 $ 64,568
Accumulated depreciation 42,293 44,465
Property and equipment, net 22,341 20,103
Equipment    
Property Plant And Equipment [Line Items]    
Property and equipment 43,038 49,349
Accumulated depreciation 31,813 34,754
Property and equipment, net 11,225 14,595
Other property and equipment    
Property Plant And Equipment [Line Items]    
Property and equipment 21,596 15,219
Accumulated depreciation 10,480 9,711
Property and equipment, net $ 11,116 $ 5,508