Certain Balance Sheet Components



Accounts receivable, net	December 31, 2015		December 31, 2014
	(in thousands)
Trade receivables (net of allowance of $5,949 and $6,195)	$	298,550	$	321,309
Unbilled receivables	32,345		25,238
Total accounts receivable, net	$	330,895	$	346,547

At December 31, 2015 and 2014, $688,000 and $4.7 million were recorded within trade receivables as billed but not yet paid by customers in accordance with contract retainage provisions. At December 31, 2015 and 2014, contract retainage amounts that were unbilled and classified as unbilled receivables were $3.5 million and $4.0 million. These contract retainage amounts within trade receivables and unbilled receivables are expected to be collected within the following 12 months.

At December 31, 2015 and 2014, long-term unbilled receivables totaled $3.6 million and $4.3 million. These long-term unbilled receivables are classified within other long-term assets, as collection is not anticipated within the following 12 months. We had $360,000 of long-term billed contract retainage receivables at December 31, 2015 and none at December 31, 2014.



Allowance for doubtful account activity	Year Ended December 31,
	2015			2014
	(in thousands)
Beginning balance	$	6,195		$	8,643
Provision for doubtful accounts, net	1,025			(31		)
Accounts written-off	(549		)	(1,883		)
Effects of change in exchange rates	(722		)	(534		)
Ending balance	$	5,949		$	6,195



Inventories	December 31, 2015		December 31, 2014
	(in thousands)
Materials	$	111,191	$	90,557
Work in process	9,400		8,991
Finished goods	69,874		54,673
Total inventories	$	190,465	$	154,221

Our inventory levels may vary period to period as a result of our factory scheduling and the timing of contract fulfillments, which may include the buildup of finished goods for shipment.

Consigned inventory is held at third-party locations; however, we retain title to the inventory until purchased by the third-party. Consigned inventory, consisting of raw materials and finished goods, was $2.6 million and $2.5 million at December 31, 2015 and 2014, respectively.



Property, plant, and equipment, net	December 31, 2015			December 31, 2014
	(in thousands)
Machinery and equipment	$	289,015		$	287,448
Computers and software	104,310			100,212
Buildings, furniture, and improvements	127,531			134,461
Land	19,882			21,759
Construction in progress, including purchased equipment	32,639			20,583
Total cost	573,377			564,463
Accumulated depreciation	(383,121		)	(357,311		)
Property, plant, and equipment, net	$	190,256		$	207,152



Depreciation expense	Year Ended December 31,
	2015		2014		2013
	(in thousands)
Depreciation expense	$	44,320	$	54,435	$	57,227