Our property, plant and equipment, net, consisted of the following (in thousands):

	March 31,			December 31,
	2019			2018
Machinery, equipment, vehicles and office furniture	$	6,584,307		$	6,328,966
Tooling		1,418,368			1,397,514
Leasehold improvements		987,916			960,971
Land and buildings		2,631,607			4,047,006
Computer equipment, hardware and software		525,138			487,421
Construction in progress		622,180			807,297
		12,769,516			14,029,175
Less: Accumulated depreciation		(2,918,587	)		(2,699,098	)
Total	$	9,850,929		$	11,330,077

As of December 31, 2018, the table above included $1.69 billion of gross build-to-suit lease assets. As a result of the adoption of the new lease standard on January 1, 2019, we have de-recognized all build-to-suit lease assets and have reassessed these leases to be operating lease right-of-use assets within the consolidated balance sheet as of March 31, 2019 (see Note 2, Summary of Significant Accounting Policies). This includes construction in progress associated with certain build-to-suit lease costs incurred at our Buffalo manufacturing facility, referred to as Gigafactory 2.

Construction in progress is primarily comprised of tooling and equipment related to the manufacturing of our vehicles and a portion of Gigafactory 1 construction. Completed assets are transferred to their respective asset classes, and depreciation begins when an asset is ready for its intended use. Interest on outstanding debt is capitalized during periods of significant capital asset construction and amortized over the useful lives of the related assets. During the three months ended March 31, 2019 and 2018, we capitalized $7.5 million and $18.8 million, respectively, of interest.

Depreciation expense during the three months ended March 31, 2019 and 2018 was $299.4 million and $245.2 million, respectively. Gross property and equipment under finance leases as of March 31, 2019 and December 31, 2018 was $1.72 billion and $1.52 billion, respectively. Accumulated depreciation on property and equipment under finance leases as of these dates was $276.8 million and $231.6 million, respectively.

Panasonic has partnered with us on Gigafactory 1 with investments in the production equipment that it uses to manufacture and supply us with battery cells. Under our arrangement with Panasonic, we plan to purchase the full output from their production equipment at negotiated prices. As these terms convey a finance lease, as defined in ASC 842, Leases, their production equipment, we consider them to be leased assets when production commences. This results in us recording the cost of their production equipment within property, plant and equipment, net, on the consolidated balance sheets with a corresponding liability recorded to long-term debt and finance leases. For all suppliers and partners for which we plan to purchase the full output from their production equipment located at Gigafactory 1, we have applied similar accounting. As of March 31, 2019 and December 31, 2018, we had cumulatively capitalized costs of $1.41 billion and $1.24 billion, respectively, on the consolidated balance sheets in relation to the production equipment under our Panasonic arrangement. We had cumulatively capitalized total costs for Gigafactory 1, including costs under our Panasonic arrangement, of $4.92 billion and $4.62 billion as of March 31, 2019 and December 31, 2018, respectively.