Property and Equipment, net

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment, Net [Abstract]

Property and equipment comprised the following as of December 31, 2018 and 2017 (in thousands):



	December 31,
	2018			2017
Property and equipment–at cost:
Plant and machinery	$	15,206		$	13,762
Instruments	15,089			13,347
Office equipment	2,114			1,948
Leasehold improvements	10,648			10,480
Total property and equipment–at cost	43,057			39,537
Accumulated depreciation and amortization	(21,987		)	(16,956		)
Total property and equipment, net	$	21,070		$	22,581

Depreciation expense was $5,919,000, $4,771,000 and $3,510,000 for the years ended December 31, 2018, 2017 and 2016, respectively. During the years ended December 31, 2018, 2017 and 2016, the Company disposed of certain assets no longer in use with a net book value of $501,000, $207,000, and $76,000, respectively, recorded to cost of revenue, sales and marketing, research and development, or general and administrative expenses based on the asset's respective use.