Balance Sheets Details

Accounts receivable

The following is a summary of activity in our allowance for doubtful accounts for the periods presented (in thousands):



	December 31,
	2018			2017			2016
Allowance - beginning of period	$	(34	)	$	(421	)	$	(421	)
Write-offs and other ⁽¹⁾	—			387			—
Allowance - end of period	$	(34	)	$	(34	)	$	(421	)

⁽¹⁾ The change in allowance for doubtful accounts was mainly related to the write-off of receivables from a foreign customer.

Inventories

Inventories consisted of the following (in thousands):

Property and Equipment, net

Property and equipment, net consisted of the following (in thousands):



	December 31,
	2018			2017
Laboratory equipment ⁽¹⁾	$	21,328		$	19,777
Leasehold improvements	10,359			10,327
Computer equipment and software	3,954			3,695
Office equipment and furniture	1,272			1,185
Construction in progress ⁽²⁾	939			85
Property and equipment	37,852			35,069
Less: accumulated depreciation and amortization	(33,093		)	(32,254		)
Property and equipment, net	$	4,759		$	2,815

⁽¹⁾ Fully depreciated laboratory equipment with a cost of $0.3 million and $0.2 million were retired during 2018 and 2017, respectively.

⁽²⁾ Construction in progress includes equipment received but not yet placed into service pending installation.

Goodwill

Goodwill had a carrying value of approximately of $3.2 million as of December 31, 2018 and 2017.

Other Accrued Liabilities

Other accrued liabilities consisted of the following (in thousands):



	December 31,
	2018		2017
Accrued purchases	$	1,492	$	941
Accrued professional and outside service fees	2,020		2,393
Deferred rent	343		258
Lease incentive obligation	425		425
Other	575		345
Total	$	4,855	$	4,362