The reconciliation of cash, cash equivalents and restricted cash reported on the condensed consolidated balance sheets to the total of the same such amounts in the condensed consolidated statements of cash flows is as follows (in thousands):


	June 30, 2021		December 31, 2020
Cash and cash equivalents	$	893,688	$	893,219
Restricted cash included in other assets	4,236		4,235
Total cash, cash equivalents and restricted cash	$	897,924	$	897,454


	June 30, 2021		December 31, 2020
Accounts receivable	$	368,817	$	394,037
Allowance for doubtful accounts	(587)		(659)
Product sales rebate and returns reserve	(4,016)		(3,838)
Accounts receivable, net	$	364,214	$	389,540


	June 30, 2021		December 31, 2020
Raw materials	$	271,055	$	219,218
Finished goods	272,144		260,450
Total inventories	$	543,199	$	479,668


	June 30, 2021		December 31, 2020
Inventory deposits	$	22,386	$	18,783
Prepaid income taxes	18,479		267
Other current assets	81,017		60,556
Other prepaid expenses and deposits	17,397		15,316
Total prepaid expenses and other current assets	$	139,279	$	94,922


	June 30, 2021		December 31, 2020
Equipment and machinery	$	77,361	$	70,655
Computer hardware and software	43,087		40,081
Leasehold improvements	30,502		31,448
Furniture and fixtures	3,592		3,787

Construction-in-process	1,214		1,441
Property and equipment, gross	155,756		147,412
Less: accumulated depreciation	(123,394)		(115,181)
Property and equipment, net	$	32,362	$	32,231

Depreciation expense was $4.8 million and $5.1 million for the three months ended June 30, 2021 and 2020, respectively, and $9.7 million and $10.3 million for the six months ended June 30, 2021 and 2020, respectively.


	June 30, 2021		December 31, 2020
Accrued payroll related costs	$	64,028	$	73,634
Accrued manufacturing costs	63,260		43,181
Accrued product development costs	15,355		6,733
Accrued warranty costs	8,995		9,314
Other	11,607		10,495
Total accrued liabilities	$	163,245	$	143,357

The following table summarizes the activity related to our accrued liability for estimated future warranty costs (in thousands):


	Six Months Ended June 30,
	2021		2020
Warranty accrual, beginning of period	$	9,314	$	6,742
Liabilities accrued for warranties issued during the period	5,603		2,181
Warranty costs incurred during the period	(5,922)		(2,852)
Warranty accrual, end of period	$	8,995	$	6,071

The following table summarizes the beginning and ending balances of our contract assets included in "Prepaid and other current assets" on the condensed consolidated balance sheets (in thousands):


	Six Months Ended June 30,
	2021
Contract assets, beginning balance	$	16,380
Contract assets, ending balance	11,935

A contract liability is recognized when we have received customer payments in advance of our satisfaction of a performance obligation under a cancellable contract. The following table summarizes the activity related to our contract liabilities (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Contract liabilities, beginning balance	$	80,465	$	64,325	$	85,957	$	61,050
Less: Revenue recognized from beginning balance	(8,482)		(5,735)		(18,482)		(11,722)
Less: Beginning balance reclassified to deferred revenue	(3,856)		(2,757)		(12,710)		(2,226)
Add: Contract liabilities recognized	15,227		11,435		28,589		20,166
Contract liabilities, ending balance	$	83,354	$	67,268	$	83,354	$	67,268

As of June 30, 2021 and December 31, 2020, $35.9 million and $34.5 million of our contract liabilities, respectively, were included in "Other current liabilities" with the remaining balances included in "Other long-term liabilities" on the condensed consolidated balance sheets.

Deferred revenue is comprised mainly of unearned revenue related to multi-year post-contract support ("PCS") contracts, services and product deferrals related to acceptance clauses. The following table summarizes the activity related to our deferred revenue (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Deferred revenue, beginning balance	$	720,031	$	596,775	$	650,827	$	575,288
Less: Revenue recognized from beginning balance	(145,556)		(104,480)		(222,865)		(178,264)
Add: Deferral of revenue in current period, excluding amounts recognized during the period	171,615		85,216		318,128		180,487
Deferred revenue, ending balance	$	746,090	$	577,511	$	746,090	$	577,511

As of June 30, 2021, other performance obligations of $169.2 million were comprised mainly of unbilled multi-year PCS contract amounts that will be recognized as revenue in future periods.

Revenue from total remaining performance obligations represents contract liabilities, deferred revenue and unbilled contract revenue that will be recognized in future periods. As of June 30, 2021, approximately $998.7 million of revenue is expected to be recognized from remaining performance obligations, of which approximately 83% is expected to be recognized over the next two years and approximately 17% is expected to be recognized during the third to the fifth year.


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Interest income	$	1,872	$	8,668	$	3,917	$	20,330


Other income (expense), net	(153)		(412)		(623)		83
Total	$	1,719	$	8,256	$	3,294	$	20,413