Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Allowance for Doubtful Accounts

Activity related to allowance for doubtful accounts consisted of the following (in thousands):

Year Ended	Balance at Beginning of Year		Provision		Write-offs			Balance at End of Year
December 31, 2017	$	535	$	471	$	(191	)	$	815
December 31, 2016	$	417	$	179	$	(61	)	$	535
December 31, 2015	$	425	$	20	$	(28	)	$	417

Estimated Useful Lives of Property and Equipment and Field Equipment

The estimated useful lives of property and equipment and field equipment are as follows:

	Estimated Useful Life
Buildings	30 years
Equipment and tooling	5 to 12 years
Leasehold improvements	Lesser of the lease term (including any renewal periods if appropriate) or estimated useful life of the asset
Computer and office equipment	3 to 5 years
Molds	5 to 7 years
Furniture	5 to 7 years
Field equipment	5 to 7 years

Rollforward of Warranty Accrual

The following is a rollforward of our warranty accrual (in thousands):

Year Ended	Balance at Beginning of Year		Provision		Usage			Balance at End of Year
December 31, 2017	$	280	$	445	$	(432	)	$	293
December 31, 2016	$	389	$	457	$	(566	)	$	280
December 31, 2015	$	287	$	526	$	(424	)	$	389