9. Supplementary Balance Sheet Information

The following is a summary of accounts receivable at September 30, 2018 and 2017 (in thousands):


	September 30,
	2018		2017
Accounts receivable	$	126,350	$	94,927
Less allowance for doubtful accounts		(1,113)		(1,381)
Less allowance for sales returns		(45)		(81)
Accounts receivable, net	$	125,192	$	93,465

The allowance for doubtful accounts activity for the fiscal years ended September 30, 2018, 2017 and 2016 is as follows (in thousands):


	Balance at				Reversals of		Write-		Balance at
	Beginning of				Bad Debt		offs and		End of
Description	Period		Provisions		Expense		Adjustments		Period
2018 Allowance for doubtful accounts	$	1,381	$	708	$	(724)	$	(252)	$	1,113
2017 Allowance for doubtful accounts		1,543		—		(131)		(31)		1,381
2016 Allowance for doubtful accounts		332		143		48		1,020		1,543

The allowance for sales returns activity for the fiscal years ended September 30, 2018, 2017 and 2016 is as follows (in thousands):


	Balance at				Write-		Balance at
	Beginning of				offs and		End of
Description	Period		Provisions		Adjustments		Period
2018 Allowance for sales returns	$	81	$	(36)	$	—	$	45
2017 Allowance for sales returns		101		(20)		—		81
2016 Allowance for sales returns		115		(14)		—		101

The following is a summary of inventories at September 30, 2018 and 2017 (in thousands):


	September 30,
	2018		2017
Inventories
Raw materials and purchased parts	$	57,527	$	53,234
Work-in-process		19,547		7,120
Finished goods		19,912		13,043
Total inventories	$	96,986	$	73,397

The activity for excess and obsolete inventory reserves is as follows for the fiscal years ended September 30, 2018, 2017 and 2016 (in thousands):


	Balance at				Inventory		Balance at
	Beginning of				Disposals and		End of
Description	Period			Provisions	Adjustments		Period
2018 Reserves for excess and obsolete inventory	$	17,734	$	4,455	$	(7,236)	$	14,953
2017 Reserves for excess and obsolete inventory		19,663		4,858		(6,787)		17,734
2016 Reserves for excess and obsolete inventory		19,603		5,754		(5,694)		19,663

The activity for valuation allowance for deferred tax assets is as follows for the fiscal years ended September 30, 2018, 2017 and 2016 (in thousands):


	Balance at						Balance at
	Beginning of		Charged to		Charged to		End of
Description	Period		Provisions		Other Accounts		Period
2018 Valuation allowance for deferred tax assets	$	92,297	$	(72,842)	$	(874)	$	18,581
2017 Valuation allowance for deferred tax assets		104,802		(10,881)		(1,624)		92,297
2016 Valuation allowance for deferred tax assets		18,797		77,531		8,474		104,802

The Company establishes reserves for estimated cost of product warranties based on historical information. Product warranty reserves are recorded at the time product revenue is recognized, and retrofit accruals are recorded at the time retrofit programs are established. The Company’s warranty obligation is affected by product failure rates, utilization levels, material usage, service delivery costs incurred in correcting a product failure and supplier warranties on parts delivered to the Company. The following is a summary of product warranty and retrofit activity on a gross basis, excluding amounts related to discontinued operations, for the fiscal years ended September 30, 2018, 2017 and 2016 (in thousands):


	Amount
Balance at September 30, 2015	$	4,255
Accruals for warranties during the year		5,851
Costs incurred during the year		(5,947)
Balance at September 30, 2016		4,159
Accruals for warranties during the year		6,683
Costs incurred during the year		(5,363)
Balance at September 30, 2017		5,479
Accruals for warranties during the year		5,209
Costs incurred during the year		(4,348)
Balance at September 30, 2018	$	6,340