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,
	2017			2016
Balance at beginning of period	$	811		$	746
Bad debt expense (recovery)	(160		)	187
Uncollectible accounts written off, net of recoveries	(472		)	(120		)
Change due to foreign currency translation	—			(2		)
Balance at end of period	$	179		$	811

Inventories

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



	September 30,
	2017			2016
Raw materials, parts and subassemblies	$	22,100		$	29,639
Work-in-progress	600			996
Provision for excess and obsolete inventory	(4,252		)	(4,114		)
Total inventories	$	18,448		$	26,521

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,
	2017			2016
Costs incurred on uncompleted contracts	$	987,164		$	1,088,921
Estimated earnings	316,970			350,125
	1,304,134			1,439,046
Less: Billings to date	(1,278,746		)	(1,416,914		)
Net underbilled position	$	25,388		$	22,132
Included in the accompanying balance sheets under the following captions:
Costs and estimated earnings in excess of billings on uncompleted contracts – underbilled	$	51,554		$	66,106
Billings in excess of costs and estimated earnings on uncompleted contracts – overbilled	(26,166		)	(43,974		)
Net underbilled position	$	25,388		$	22,132

Property, Plant and Equipment

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



	September 30,						Range of
	2017			2016			Asset Lives
Land	$	22,441		$	22,107		—
Buildings and improvements	121,960			119,512			3 - 39 Years
Machinery and equipment	106,113			103,268			3 - 15 Years
Furniture and fixtures	3,806			3,806			3 - 10 Years
Construction in process	1,749			1,009			—
	$	256,069		$	249,702
Less: Accumulated depreciation	(116,649		)	(104,725		)
Total property, plant and equipment, net	$	139,420		$	144,977

There were no assets under capital lease as of September 30, 2017 or September 30, 2016. Depreciation expense was $12.4 million, $13.0 million and $13.1 million for fiscal years 2017, 2016, and 2015, respectively.

Warranty Accrual

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



	September 30,
	2017			2016
Balance at beginning of period	$	4,639		$	4,930
Increase to warranty expense	1,806			4,249
Deduction for warranty charges	(3,314		)	(4,464		)
Change due to foreign currency translation	43			(76		)
Balance at end of period	$	3,174		$	4,639