The following table is a reconciliation of cash, cash equivalents and restricted cash reported within the accompanying condensed consolidated balance sheets that sum to the total of the same such amounts shown in the accompanying condensed consolidated statements of cash flows (in thousands):



	June 30, 2019		June 30, 2018
Cash and cash equivalents	$	944,414	$	711,157
Restricted cash included in other assets	4,222		5,512
Total cash, cash equivalents and restricted cash	$	948,636	$	716,669

Restricted cash included in other assets as of June 30, 2019 and June 30, 2018 primarily included $4.0 million pledged as collateral representing a security deposit required for a facility lease. In addition, restricted cash included in other assets as of June 30, 2018 included $1.1 million related to a letter of credit issued to a business partner.



	June 30, 2019			December 31, 2018
Accounts receivable	$	350,568		$	340,897
Allowance for doubtful accounts	(837		)	(507		)
Product sales rebate and returns reserve	(6,651		)	(8,613		)
Accounts receivable, net	$	343,080		$	331,777



	June 30, 2019		December 31, 2018
Prepaid income taxes	$	43,464	$	38,636
Inventory deposit	14,250		14,639
Other current assets	43,665		95,730
Other prepaid expenses and deposits	12,079		13,316
Total prepaid expenses and other current assets	$	113,458	$	162,321



	June 30, 2019			December 31, 2018
Equipment and machinery	$	59,720		$	55,912
Computer hardware and software	33,229			30,566
Leasehold improvements	31,402			36,447
Furniture and fixtures	3,736			3,697
Building	—			35,154
Construction-in-process	959			3,591
Property and equipment, gross	129,046			165,367
Less: accumulated depreciation	(88,023		)	(90,012		)
Property and equipment, net	$	41,023		$	75,355

On January 1, 2019, upon the adoption of ASC 842, we derecognized the building and certain leasehold improvements that were capitalized for our corporate headquarters building under a build-to-suit arrangement. See Note 1 and Note 6 for further details.

Depreciation expense was $4.8 million and $5.4 million for the three months ended June 30, 2019 and 2018, respectively, and $9.5 million and $10.7 million for the six months ended June 30, 2019 and 2018, respectively.



	June 30, 2019		December 31, 2018
Accrued payroll related costs	$	55,957	$	70,755
Accrued manufacturing costs	30,318		31,336
Accrued product development costs	12,189		6,988
Accrued professional fees	6,312		5,678
Accrued warranty costs	5,074		5,362
Other	4,048		3,135
Total accrued liabilities	$	113,898	$	123,254



	Six Months Ended June 30,
	2019			2018
Warranty accrual, beginning of period	$	5,362		$	7,415
Liabilities accrued for warranties issued during the period	2,082			3,813
Warranty costs incurred during the period	(2,370		)	(3,046		)
Warranty accrual, end of period	$	5,074		$	8,182



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Contract assets, beginning balance	$	5,699	$	—	$	6,341	$	—
Contract assets, ending balance	1,668		6,959		1,668		6,959



	Three Months Ended June 30,						Six Months Ended June 30,
	2019			2018			2019			2018
Contract liabilities, beginning balance	$	37,314		$	18,838		$	32,595		$	16,521
Less: Revenue recognized from beginning balance	(3,552		)	(1,933		)	(6,766		)	(4,070		)
Less: Beginning balance reclassified to deferred revenue	(1,593		)	(906		)	(1,205		)	(731		)
Add: Contract liabilities recognized	9,857			5,843			17,402			10,122
Contract liabilities, ending balance	$	42,026		$	21,842		$	42,026		$	21,842

As of June 30, 2019 and December 31, 2018, $16.7 million and $13.5 million of our contract liabilities, respectively, was included in “Other current liabilities” with the remaining balances included in “Other long-term liabilities”.

Deferred revenue is comprised mainly of unearned revenue related to multi-year 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,
	2019			2018			2019			2018
Deferred revenue, beginning balance⁽¹⁾	$	536,471		$	456,054		$	587,227		$	498,740
Less: Revenue recognized from beginning balance	(119,542		)	(112,998		)	(253,616		)	(238,557		)
Add: Deferral of revenue in current period, excluding amounts recognized during the period	85,289			105,588			168,607			188,461
Deferred revenue, ending balance	$	502,218		$	448,644		$	502,218		$	448,644
______________________
(1) The beginning balance of the six months ended June 30, 2018 excludes $16.5 million that was reclassified to other current liabilities and other long-term liabilities at January 1, 2018 as a result of our adoption of ASC 606.

Revenue from remaining performance obligations represents contracted revenue that has not yet been recognized, which includes contract liabilities and deferred revenue that will be recognized as revenue in future periods. As of June 30, 2019, approximately $545.7 million of revenue is expected to be recognized from remaining performance obligations. We expect to recognize revenue on approximately 83% of these remaining performance obligations over the next 2 years and 17% during the 3rd to the 5th year.



	Three Months Ended June 30,					Six Months Ended June 30,
	2019		2018			2019			2018
Interest income	$	13,107	$	7,964		$	25,005		$	13,348
Interest expense	—		(680		)	—			(1,367		)
Gain (loss) on investment in privately-held companies	—		(9,100		)	1,150			(9,100		)
Other income (expense), net	704		(353		)	(11		)	(894		)
Total	$	13,811	$	(2,169	)	$	26,144		$	1,987

Upon the adoption of ASC 842 on January 1, 2019, we derecognized the lease financing obligation associated with a build-to-suit lease, and therefore did not incur interest expense in the three and six months ended June 30, 2019. See Note 1 for further details.