3. Balance Sheet Details

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


	June 30,		December 31,
	2018		2018
Accounts receivable	$	225,336	$	240,749
Less allowance for doubtful accounts		(14,592)		(14,663)
Total	$	210,744	$	226,086


	June 30,		December 31,
	2018		2018
Raw materials	$	156,612	$	153,195
Work-in-process		89,468		86,582
Finished goods		67,472		75,423
Total	$	313,552	$	315,200


	June 30,		December 31,
	2018		2018
Land	$	16,569	$	16,555
Buildings, civil works and improvements		56,585		55,083
Leasehold improvements		9,681		10,144
Equipment and tooling		117,294		125,099
Furniture and fixtures		3,331		3,175
Computer equipment		18,759		17,863
Computer software		19,509		19,555
Computer software implementation in process		4,318		6,640
Construction in process		790		2,428
Total		246,836		256,542
Less accumulated depreciation and amortization		(131,312)		(135,272)
Property and equipment, net	$	115,524	$	121,270

Depreciation expense was $16.8 million and $5.2 million for the three months ended December 31, 2017 and 2018, respectively, and approximately $33.0 million and $10.3 million for the six months ended December 31, 2017 and 2018, respectively. The decrease in depreciation is primarily related to a transfer of assets.

In January 2018, we entered into a two-year agreement with the Mexican government to continue providing security screening services. Upon inception of the contract, we transferred certain fixed assets with a net book value of $29.5 million to the customer, and this remaining cost to obtain the contract is amortized on a straightline basis over the term of the contract as corresponding revenues are recognized. During the three and six months ended December 31, 2018, we recognized $3.7 million and $7.1 million, respectively, of amortization expense related to such assets. As of December 31, 2018, $13.7 million and $0.5 million, respectively, are recorded within Prepaid expenses and other current assets and Other assets.