Annual report pursuant to Section 13 and 15(d)

Schedule II: Valuation and Qualifying Accounts (Details)

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Schedule II: Valuation and Qualifying Accounts (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Allowance for Doubtful Accounts      
Valuation And Qualifying Accounts Disclosure [Line Items]      
Balance Beginning of Year $ 1,869 $ 1,664 $ 1,180
Additions 3,864 3,580 2,680
Deletions 4,418 2,575 2,196
Adjustments 100 (800)  
Balance at End of Year 1,415 1,869 1,664
Allowance for Sales Returns      
Valuation And Qualifying Accounts Disclosure [Line Items]      
Balance Beginning of Year 585 366 173
Additions 9,909 7,502 4,918
Deletions 9,590 7,283 4,725
Balance at End of Year 904 585 366
Allowance for Rental Revenue Adjustments      
Valuation And Qualifying Accounts Disclosure [Line Items]      
Balance Beginning of Year 6,078 4,115 2,392
Additions 5,057 10,777 8,543
Deletions 10,088 9,614 6,820
Adjustments (100) 800  
Balance at End of Year 947 6,078 4,115
Allowance for Inventory Reserves      
Valuation And Qualifying Accounts Disclosure [Line Items]      
Balance Beginning of Year 191 128 141
Additions 340 133 89
Deletions 132 70 102
Balance at End of Year 399 191 128
Allowance for Rental Asset Loss      
Valuation And Qualifying Accounts Disclosure [Line Items]      
Balance Beginning of Year 725 850 832
Additions 561 455 498
Deletions 532 580 480
Balance at End of Year $ 754 $ 725 $ 850