As of June 30, 2021, the short-term restricted cash balance of $0.3 million was comprised of a security deposit for the credit cards of employees. As of December 31, 2020, the short-term restricted cash balance of $0.8 million was comprised of $0.5 million for a customer deposit and $0.3 million for the security deposit for the credit cards of employees.

As of June 30, 2021 and December 31, 2020, our inventory consisted of the following components:



	June 30,		December 31,
(in thousands)	2021		2020
Purchased materials	$	5,253	$	3,531
Work in process		9,050		6,651
Finished goods		3,682		4,048
Inventory	$	17,985	$	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, beginning on May 1, 2019, the amount of the letter of credit was reduced by $0.5 million each year thereafter on May 1. As such, $3.0 million and $3.5 million was recorded in long-term restricted cash in the condensed consolidated balance sheets as of June 30, 2021 and December 31, 2020, respectively.

As of June 30, 2021, we had a total of $19.7 million of deferred revenue, $9.5 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 $10.2 million was recorded as deferred revenue, non-current. Of the deferred revenue, non-current balance, $1.5 million primarily relates to our service contracts and is scheduled to be recognized in the next 5 years and $8.7 million relates to payments received under the Invitae collaboration described in Note 2. Revenue recorded in the six months ended June 30, 2021 includes $5.5 million of previously deferred revenue that was included in deferred revenue, current as of December 31, 2020. Contract assets as of June 30, 2021 and December 31, 2020 were not material.

As of June 30, 2021, we had a total of $0.7 million of deferred commissions included in prepaid expenses and other current assets which is recognized as sales, general and administrative expense as the related revenue is recognized. Costs to obtain a contract are expensed as incurred if the amortization period would have been a year or less.