Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Summary of Depreciation and Amortization Expense of Rental Equipment and Other Property and Equipment (Details)

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Summary of Significant Accounting Policies - Summary of Depreciation and Amortization Expense of Rental Equipment and Other Property and Equipment (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Property Plant And Equipment [Line Items]      
Depreciation $ 9,835 $ 11,429 $ 11,965
Depreciation and amortization 11,795 13,457 13,926
Equipment      
Property Plant And Equipment [Line Items]      
Depreciation 9,835 11,429 11,965
Other property and equipment      
Property Plant And Equipment [Line Items]      
Depreciation and amortization $ 1,960 $ 2,028 $ 1,961