Note 3. Balance Sheet Details

Short-term investments

Short-term investments consisted of the following (in thousands):


	At March 31, 2018
	Maturity	Amortized cost		Unrealized		Unrealized		Estimated
	(in years)	or cost		gains		losses		fair value
U.S. government bonds	less than 2	$	1,799	$	-	$	(16)	$	1,783
U.S. government agency bonds	less than 2		4,185		-		(24)		4,161
Bank certificates of deposit	less than 1		11,800		-		(8)		11,792
Commercial paper	less than 1		16,178		-		(6)		16,172
Corporate notes	less than 3		46,381		2		(243)		46,140
Asset-backed securities	less than 3		18,262		-		(133)		18,129
Total		$	98,605	$	2	$	(430)	$	98,177

	At December 31, 2017
	Maturity	Amortized cost		Unrealized		Unrealized		Estimated
	(in years)	or cost		gains		losses		fair value
U.S. government bonds	less than 2	$	1,799	$	-	$	(17)	$	1,782
U.S. government agency bonds	less than 2		2,698		-		(17)		2,681
Bank certificates of deposit	less than 1		10,300		1		(3)		10,298
Commercial paper	less than 1		11,598		-		(5)		11,593
Corporate notes	less than 3		51,532		6		(121)		51,417
Asset-backed securities	less than 3		16,796		-		(61)		16,735
Total		$	94,723	$	7	$	(224)	$	94,506

Accounts receivable, net

Accounts receivable consisted of the following (in thousands):


	March 31,		December 31,
	2018		2017
Accounts receivable	$	18,198	$	17,248
Less allowance for doubtful accounts		(649)		(592)
	$	17,549	$	16,656

Inventory, net

Inventory consisted of the following (in thousands):

Accrued liabilities

Accrued liabilities consisted of the following (in thousands):


	March 31,		December 31,
	2018		2017
Accrued contract payments (see Note 9)	$	999	$	1,033
Accrued bonuses		3,168		9,106
Accrued vacation benefits		2,211		2,121
Accrued Employee Stock Purchase Plan liability		1,384		1,517
Other accrued liabilities		5,943		6,672
	$	13,705	$	20,449