4.	Balance Sheet Details

Short-Term

Investments

The following is a summary of our short-term investments (in thousands):

	December 31, 201 8
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
U.S. treasury bills and government agency obligations	$	59,747	$	—	$	(6	)	$	59,741
U.S. corporate debt		59,164		—		(77	)		59,087
Foreign corporate debt		5,041		5		—			5,046
U.S. commercial paper		52,800		—		—			52,800
Foreign commercial paper		123,870		—		(9	)		123,861
Total	$	300,622	$	5	$	(92	)	$	300,535

	December 31, 201 7
			Gross		Gross
	Amortized		Unrealized		Unrealized			Estimated
	Cost		Gains		Losses			Fair Value
U.S. corporate debt securities	$	13,003	$	—	$	(10	)	$	12,993
U.S. commercial paper		4,929		—		—			4,929
Foreign commercial paper		9,874		—		—			9,874
Total	$	27,806	$	—	$	(10	)	$	27,796

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, 2018

and

2017.

Inventory

Inventory consists of the following (in thousands):

	December 31,
	2018		2017
Raw materials	$	10,112	$	2,754
Work in process		20,604		4,166
Finished goods		8,316		3,188
Total inventory	$	39,032	$	10,108

As of

December 31, 2018,

total inventory included

$6.7

million related to SUSTOL and

$32.3

million related to CINVANTI. As of

December 31, 2017,

total inventory included

$7.1

million related to SUSTOL and

$3.0

million related to CINVANTI.

Property and Equipment

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

	December 31,
	2018			2017
Scientific equipment	$	18,077		$	9,742
Leasehold improvements		1,783			1,654
Computer equipment and software		1,190			1,420
Furniture, fixtures and office equipment		1,722			1,024
Property and equipment, gross		22,772			13,840
Less: accumulated depreciation and amortization		(8,095	)		(7,859	)
Property and equipment, net	$	14,677		$	5,981

Depreciation and amortization expense for the years ended

December

31,

2018,

2017

and

2016

was

$1.5

million,

$1.5

million and

$1.1

million, respectively. As of

December 31, 2018

and

2017,

$10.3

million and

$2.0

million of property and equipment, respectively, was in process and

not

depreciated during the respective years.

Accrued Payroll and Employee Liabilities and Other Accrued

Liabilities

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

	December 31,
	20 18		2017
Accrued employee salaries and benefits	$	2,330	$	1,292
Accrued bonuses		9,139		5,044
Accrued vacation		1,928		1,438
Accrued expenses for realignment (see Note 7)		—		1,086
Total accrued payroll and employee liabilities	$	13,397	$	8,860

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

	December 31,
	2018		2017
Accrued product sales allowances	$	25,503	$	9,319
Accrued consulting and professional fees		5,768		6,869
Deferred rent		780		651
Accrued accounts payable		224		148
Other accrued liabilities		440		188
Total other accrued liabilities	$	32,715	$	17,175