As of March 31, 2021 and December 31, 2020, the short-term restricted cash balance of $0.8 million was comprised of $0.5 million of a customer deposit and $0.3 million of the security deposit for the credit cards for employees.

As of March 31, 2021 and December 31, 2020, our inventory consisted of the following components:



	March 31,		December 31,
(in thousands)	2021		2020
Purchased materials	$	4,458	$	3,531
Work in process		6,862		6,651
Finished goods		4,948		4,048
Inventory	$	16,268	$	14,230

For our facility located at 1305 O’Brien Drive, Menlo Park, California (the “O’Brien Lease”), we were required to establish a letter of credit for the benefit of the landlord and to submit $4.5 million as a deposit for the letter of credit in October 2015. Subsequently, pursuant to the terms of the O’Brien Lease, on May 1, 2019, the amount of the letter of credit was reduced from $4.5 million to $4.0 million and in May 2020 was reduced to $3.5 million. As such, $3.5 million was recorded in “Long-term restricted cash” in the condensed consolidated balance sheet as of March 31, 2021 and December 31, 2020.

As of March 31, 2021, we had a total of $15.3 million of deferred revenue, $9.6 million of which was recorded as “Deferred revenue, current” and primarily relates to our service contracts to be recognized over the next year and the remaining $5.7 million was recorded as “Deferred revenue, non-current.” Of the “Deferred revenue, non-current” balance, $1.6 million primarily relates to our service contracts and is scheduled to be recognized in the next 5 years, while $4.1 million relates to payments received under the Invitae collaboration described in Note 2. Revenue recorded in the three months ended March 31, 2021 includes $3.1 million of previously deferred revenue that was included in “Deferred revenue, current” as of December 31, 2020. Contract assets as of March 31, 2021 and December 31, 2020 were not material.

As of March 31, 2021, we had a total of $0.7 million of deferred commissions included in “Prepaid expenses and other current assets” which is recognized as the related revenue is recognized. Additionally, as a practical expedient, we expense costs to obtain a contract as incurred if the amortization period would have been a year or less.