4.	Balance Sheet Details

Short-Term Investments

The following is a summary of our short-term, available-for-sale securities (in thousands):

	December 31, 201 6
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
United States corporate debt	$	12,048	$	—	$	(9	)	$	12,039
Foreign corporate debt		14,065		—		(8	)		14,057
United States commercial paper		8,635		—		—			8,635
Foreign commercial paper		2,993		—		—			2,993
Total	$	37,741	$	—	$	(17	)	$	37,724

	December 31, 201 5
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
United States corporate debt	$	27,750	$	—	$	(35	)	$	27,715
Foreign corporate debt		4,927		—		(5	)		4,922
United States commercial paper		7,770		—		—			7,770
Foreign commercial paper		15,579		—		—			15,579
Total	$	56,026	$	—	$	(40	)	$	55,986

The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. We regularly monitor and evaluate the realizable value of our marketable securities. We did not recognize any impairment losses for the years ended

December

31,

2016

and

2015.

Inventory

Inventory consists of the following (in thousands):

	December 31,
	2016		2015
Raw materials	$	1,647	$	—
Work in process		1,104		—
Finished goods		2,589		—
Total inventory	$	5,340	$	—

Property and Equipment

Property and equipment consists of the following (in thousands):

	December 31,
	2016			2015
Scientific equipment	$	7,952		$	5,593
Computer equipment and software		1,429			1,272
Furniture, fixtures and office equipment		674			352
Leasehold improvements		1,635			1,384
Property and equipment		11,690			8,601
Less: accumulated depreciation and amortization		(6,614	)		(5,552	)
Property and equipment, net	$	5,076		$	3,049

Depreciation and amortization expense for the years ended

December

31,

2016,

2015

and

2014

was

$1.1

million,

$0.7

million and

$0.6

million, respectively. As of

December

31,

2016

and

2015,

$1.7

million and

$0.2

million of property and equipment, respectively, were in process and not depreciated during the respective years.

During the year ended

December

31,

2014,

we recognized

$0.9

million as an impairment loss due to the write-down of a piece of manufacturing-related equipment. In

2015,

we sold the equipment for cash proceeds of

$0.2

million, with a net gain of

$0.1

million.

Accrued Payroll and Employee Liabilities and Other Accrued

Liabilities

Accrued payroll and employee liabilities consist of the following (in thousands):

	December 31,
	20 16		2015
Accrued employee salaries and benefits	$	2,236	$	1,863
Accrued bonuses		3,474		2,965
Accrued expenses for realignment (see Note 6)		2,704		—
Total accrued payroll and employee liabilities	$	8,414	$	4,828

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

	December 31,
	2016		2015
Accrued consulting and professional fees	$	4,703	$	3,914
Accrued accounts payable		1,039		36
Accrued sales allowances		342		—
Deferred rent		116		61
Other accrued liabilities		88		143
Total other accrued liabilities	$	6,288	$	4,154