Balance sheet detail as of September 30, 2021 and December 31, 2020 is as follows (in thousands):

	September 30, 2021		December 31, 2020
Raw materials	$	33,012	$	16,962
Work in process		832		1,486
Finished goods		24,426		21,124
Total inventories	$	58,270	$	39,572

Inventories are stated at the lower of cost or net realizable value, with cost being computed based on an adjusted standard basis, which approximates actual cost on an average or first-in, first-out basis. The Company had no inventories provided as collateral for borrowings from Export-Import Bank of Korea as of September 30, 2021 compared to $9.6 million as of December 31, 2020.

	September 30, 2021			December 31, 2020
Property, plant and equipment, net:
Machinery and equipment	$	13,866		$	13,656
Leasehold improvements		5,202			4,633
Computers and software		3,133			2,829
Furniture and fixtures		1,685			1,123
Construction in progress and other		2,386			716
		26,272			22,957
Less: accumulated depreciation and amortization		(16,794	)		(15,445	)
Less: government grants		(222	)		(366	)
Total property, plant and equipment, net	$	9,256		$	7,146

Depreciation expense associated with property, plant and equipment for the three and nine months ended September 30, 2021 was $0.7 million and $2.3 million, respectively. Depreciation expense associated with property, plant and equipment for the three and nine months ended September 30, 2020 was $0.6 million and $1.6 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:

	Nine Months Ended September 30,
	2021			2020
Balance at the beginning of the period	$	1,522		$	1,610
Charged to cost of revenue		636			341
Claims and settlements		(745	)		(1,026	)
Foreign exchange impact		68			(15	)
Balance at the end of the period	$	1,481		$	910

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 majority of the Company's performance obligations in its contracts with customers relate to contracts with duration of less than one year.

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

	Contract assets			Contract liabilities
December 31, 2020	$	6,182		$	6,871
September 30, 2021		3,466			7,536
Increase (decrease)	$	(2,716	)	$	665

The decrease in contract assets during the nine months ended September 30, 2021 was primarily due to invoicing that occurred in 2021 from unbilled balances reflected as contract assets as of December 31, 2020.

The increase in contract liabilities during the nine months ended September 30, 2021 was primarily due to amounts being invoiced for certain customers that did not yet meet the revenue recognition criteria. The amount of revenue recognized in the nine months ended September 30, 2021 that was included in the prior period contract liability balance was $3.6 million. This revenue consists of services provided to customers who had been invoiced prior to the current year. We expect to recognize approximately 61% of outstanding contract liabilities as revenue over the next 12 months and the remainder thereafter.

The balance of contract cost deferred as of September 30, 2021 and December 31, 2020 was $0.5 million, respectively. During the nine months ended September 30, 2021, the Company recorded $0.4 million in amortization related to contract cost deferred as of December 31, 2020.