Balance sheet detail as of March 31, 2021 and December 31, 2020 is as follows (in thousands):

	March 31, 2021		December 31, 2020
Raw materials	$	20,662	$	16,962
Work in process		1,128		1,486
Finished goods		19,326		21,124
Total inventories	$	41,116	$	39,572

The Company had no inventories provided as collateral for borrowings from Export-Import Bank of Korea as of March 31, 2021 compared to $9.6 million as of December 31, 2020.

	March 31, 2021			December 31, 2020
Property, plant and equipment, net:
Machinery and equipment	$	13,863		$	13,656
Leasehold improvements		4,993			4,633
Computers and software		2,835			2,829
Furniture and fixtures		1,538			1,123
Other		934			716
		24,163			22,957
Less: accumulated depreciation and amortization		(15,973	)		(15,445	)
Less: government grants		(310	)		(366	)
Total property, plant and equipment, net	$	7,880		$	7,146

Depreciation expense associated with property, plant and equipment for the three months ended March 31, 2021 and March 31, 2020 was $0.9 million and $0.5 million, respectively.

The Company receives grants from certain foreign government entities mainly to support capital expenditures in the region. Such grants are deferred and are generally refundable to the extent the Company does not utilize the funds for qualifying expenditures. Once earned, the Company records the grants as a contra amount to the assets and amortizes such amount over the useful lives of the related assets as a reduction to depreciation expense.

The Company accrues warranty costs based on historical trends for the expected material and labor costs to provide warranty services. The Company's standard warranty period is one year from the date of shipment with the ability for customers to purchase an extended warranty of up to five years from the date of shipment. The following table summarizes the activity related to the product warranty liability:

	March 31,
	2021			2020
Balance at the beginning of the quarter	$	1,522		$	1,610
Charged to cost of revenue		269			33
Claims and settlements		(267	)		(495	)
Foreign exchange impact		56			(37	)
Balance at the end of the quarter	$	1,580		$	1,111

The Company records contract assets when it has a right to consideration and records accounts receivable when it has an unconditional right to consideration. Contract liabilities consist of cash payments received (or unconditional rights to receive cash) in advance of fulfilling performance obligations.

The opening and closing balances of contract assets and contract liabilities related to contracts with customers are as follows:

	Contract assets		Contract liabilities
December 31, 2020	$	6,182	$	6,871
March 31, 2021		6,233		6,492
Increase (decrease)	$	51	$	(379	)

The increase in contract assets during the three months ended March 31, 2021 was primarily due to revenue recognition criteria being met for items not yet invoiced during the period.

The decrease in contract liabilities during the three months ended March 31, 2021 was primarily due to the revenue recognition criteria being met for previously deferred revenue, partially offset by invoiced amounts that did not yet meet the revenue recognition criteria. The amount of revenue recognized in the three months ended March 31, 2021 that was included in the prior period contract liability balance was $2.1 million. This revenue consists of services provided to customers who had been invoiced prior to the current year.

The balance of contract cost deferred as of March 31, 2021 and December 31, 2020 was $0.4 million and $0.5 million, respectively. During the three months ended March 31, 2021, the Company recorded $0.4 million in amortization related to contract cost deferred as of December 31, 2020.