2. Balance Sheet Details

The following tables provide details of selected balance sheet accounts (in thousands):

	June 30, 2013			December 31, 2013
Accounts receivable
Billed receivables	$	179,458		$	169,446
Unbilled receivables	34,636			1,493
Less allowance for doubtful accounts	(7,277		)	(6,933		)
Total	$	206,817		$	164,006

Unbilled receivables included earned but unbilled revenue.

	June 30, 2013		December 31, 2013
Inventories, net
Raw materials	$	117,416	$	116,943
Work-in-process	37,337		41,391
Finished goods	51,460		61,664
Total	$	206,213	$	219,998

	June 30, 2013			December 31, 2013
Property and equipment
Land	$	8,365		$	13,651
Buildings and improvements	102,187			161,109
Leasehold improvements	9,302			10,310
Equipment and tooling	135,437			151,869
Furniture and fixtures	3,551			3,937
Computer equipment	14,309			16,535
Computer software	15,209			15,521
Construction in process	48,713			10,585
Total	337,073			383,517
Less: accumulated depreciation and amortization	(88,044		)	(112,049		)
Property and equipment, net	$	249,029		$	271,468

Construction in process consists primarily of costs related to infrastructure in Mexico that will be depreciated when assets are placed into service.

Depreciation expense was approximately $8.5 million and $23.8 million for the six months ended December 31, 2012 and 2013, respectively, and approximately $4.8 million and $12.3 million for the three months ended December 31, 2012 and 2013, respectively.