Detail of Selected Balance Sheet Accounts

Allowance for Doubtful Accounts

Activity in our allowance for doubtful accounts consisted of the following (in thousands):



	September 30,
	2018			2017
Balance at beginning of period	$	179		$	811
Bad debt expense (recovery)	111			(160		)
Uncollectible accounts written off, net of recoveries	(125		)	(472		)
Change due to foreign currency translation	(8		)	—
Balance at end of period	$	157		$	179

Inventories

The components of inventories are summarized below (in thousands):



	September 30,
	2018			2017
Raw materials, parts and subassemblies	$	24,563		$	22,100
Work-in-progress	1,080			600
Provision for excess and obsolete inventory	(4,291		)	(4,252		)
Total inventories	$	21,352		$	18,448

Cost and Estimated Earnings on Uncompleted Contracts

The components of costs and estimated earnings and related amounts billed on uncompleted contracts are summarized below (in thousands):



	September 30,
	2018			2017
Costs incurred on uncompleted contracts	$	872,882		$	987,164
Estimated earnings	269,268			316,970
	1,142,150			1,304,134
Less: Billings to date	(1,102,779		)	(1,278,746		)
Net underbilled position	$	39,371		$	25,388
Included in the accompanying balance sheets under the following captions:
Costs and estimated earnings in excess of billings on uncompleted contracts – underbilled	$	82,545		$	51,554
Billings in excess of costs and estimated earnings on uncompleted contracts – overbilled	(43,174		)	(26,166		)
Net underbilled position	$	39,371		$	25,388

Property, Plant and Equipment

Property, plant and equipment are summarized below (in thousands):



	September 30,						Range of
	2018			2017			Asset Lives
Land	$	22,207		$	22,441		—
Buildings and improvements	123,320			121,960			3 - 39 Years
Machinery and equipment	104,542			106,113			3 - 15 Years
Furniture and fixtures	3,799			3,806			3 - 10 Years
Construction in process	357			1,749			—
	$	254,225		$	256,069
Less: Accumulated depreciation	(125,461		)	(116,649		)
Total property, plant and equipment, net	$	128,764		$	139,420

There were no assets under capital lease as of September 30, 2018 or September 30, 2017. Depreciation expense was $12.7 million, $12.4 million and $13.0 million for fiscal years 2018, 2017, and 2016, respectively.

Warranty Accrual

Activity in our warranty accrual consisted of the following (in thousands):



	September 30,
	2018			2017
Balance at beginning of period	$	3,174		$	4,639
Increase to warranty expense	2,031			1,806
Deduction for warranty charges	(2,574		)	(3,314		)
Change due to foreign currency translation	(27		)	43
Balance at end of period	$	2,604		$	3,174