Balance Sheets

Accounts receivable

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



	December 31,
	2014			2013			2012
Allowance - beginning of period	$	(460	)	$	(150	)	$	(17	)
Provisions for doubtful accounts	(11		)	(386		)	(133		)
Recoveries from bad debts	—			76			—
Write-off and other	43			—			—
Allowance - end of period	$	(428	)	$	(460	)	$	(150	)

Inventories

Inventories consisted of the following (in thousands):



	December 31,
	2014		2013
Raw materials	$	84	$	763
Work in process	65		31
Finished goods	1,246		693
Total inventories	$	1,395	$	1,487

Property and Equipment, net

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



	December 31,
	2014			2013
Laboratory equipment	$	23,002		$	23,949
Leasehold improvements	9,773			9,493
Computer equipment and software	3,262			3,196
Office equipment and furniture	1,227			1,228
Construction in progress (1)	24			41
Property and equipment	37,288			37,907
Less: accumulated depreciation and amortization	(31,452		)	(29,461		)
Impairment of laboratory equipment	(1,841		)	—
Property and equipment, net	$	3,995		$	8,446


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

Intangible Assets

Intangible assets consisted of the following (in thousands):



	December 31, 2014							December 31, 2013
	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Weighted- Average Amortization Period
															(years)
Customer relationships	$	3,098	$	(3,098	)	$	—	$	3,098	$	(3,098	)	$	—	5
Developed and core technology	1,534		(1,534		)	—		1,534		(1,534		)	—		5
Maxygen intellectual property	20,244		(14,058		)	6,186		20,244		(10,684		)	9,560		6
Total	$	24,876	$	(18,690	)	$	6,186	$	24,876	$	(15,316	)	$	9,560	6

The estimated future amortization expense to be charged to research and development through the year ending December 31, 2016 is as follows (in thousands):



Year ending December 31:	Total
2015	$	3,374
2016	2,812
	$	6,186

Goodwill

There were no changes in the carrying value of goodwill of $3,241,000 during 2014 and 2013.