8. Supplementary Balance Sheet Information

The following is a summary of accounts receivable at September 30, 2017 and 2016 (in thousands):


	September 30,		September 30,
	2017		2016
Accounts receivable	$	122,868	$	108,713
Less allowance for doubtful accounts		(1,959)		(2,241)
Less allowance for sales returns		(81)		(100)
Accounts receivable, net	$	120,828	$	106,372

The allowance for doubtful accounts activity for the fiscal years ended September 30, 2017, 2016 and 2015 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
2017 Allowance for doubtful accounts	$	2,241	$	—	$	(190)	$	(92)	$	1,959
2016 Allowance for doubtful accounts		1,019		202		—		1,020		2,241
2015 Allowance for doubtful accounts		1,031		—		—		(12)		1,019

The allowance for sales returns activity for the fiscal years ended September 30, 2017, 2016 and 2015 is as follows (in thousands):


	Balance at				Write-		Balance at
	Beginning of				offs and		End of
Description	Period		Provisions		Adjustments		Period
2017 Allowance for sales returns	$	101	$	(20)	$	—	$	81
2016 Allowance for sales returns		115		(14)		—		101
2015 Allowance for sales returns		133		(18)		—		115

The following is a summary of inventories at September 30, 2017 and 2016 (in thousands):


	September 30,		September 30,
	2017		2016
Inventories
Raw materials and purchased parts	$	73,819	$	60,979
Work-in-process		10,548		16,090
Finished goods		22,028		15,503
Total inventories	$	106,395	$	92,572

The activity for excess and obsolete inventory reserves is as follows for the fiscal years ended September 30, 2017, 2016 and 2015 (in thousands):


	Balance at				Inventory		Balance at
	Beginning of				Disposals and		End of
Description	Period			Provisions	Adjustments		Period
2017 Reserves for excess and obsolete inventory	$	24,794	$	6,636	$	(7,888)	$	23,542
2016 Reserves for excess and obsolete inventory		23,768		7,293		(6,267)		24,794
2015 Reserves for excess and obsolete inventory		26,027		7,879		(10,138)		23,768

The activity for valuation allowance for deferred tax assets is as follows for the fiscal years ended September 30, 2017, 2016 and 2015 (in thousands):


	Balance at						Balance at
	Beginning of		Charged to		Charged to		End of
Description	Period		Provisions		Other Accounts		Period
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
2015 Valuation allowance for deferred tax assets		18,354		(36)		479		18,797

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, 2017, 2016 and 2015 (in thousands):


	Amount
Balance at September 30, 2014	$	6,499
Adjustments for acquisitions and divestitures		81
Accruals for warranties during the year		9,917
Costs incurred during the year		(10,408)
Balance at September 30, 2015		6,089
Accruals for warranties during the year		9,975
Costs incurred during the year		(9,740)
Balance at September 30, 2016		6,324
Accruals for warranties during the year		10,413
Costs incurred during the year		(8,683)
Balance at September 30, 2017	$	8,054