Balance Sheet Components

Marketable Securities

The following table summarizes the unrealized gains and losses and fair value of our short term available-for-sale securities (in thousands):



	September 30, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Commercial paper	$	11,879	$	—	$	—		$	11,879
U.S. government notes	104,955		—		(233		)	104,722
Corporate bonds	372,354		77		(397		)	372,034
Total marketable securities	$	489,188	$	77	$	(630	)	$	488,635



	December 31, 2016
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Commercial paper	$	5,962	$	—	$	—		$	5,962
U.S. government notes	110,945		5		(194		)	110,756
Corporate bonds	183,455		109		(372		)	183,192
Total marketable securities	$	300,362	$	114	$	(566	)	$	299,910

As of September 30, 2017 and December 31, 2016, there have been no other-than-temporary losses on our marketable securities. None of our marketable securities have been in continuous unrealized loss positions for greater than twelve months as of September 30, 2017.

We invest in marketable securities that have maximum maturities of up to two years and are generally deemed to be low risk based on their credit ratings from the major rating agencies. The longer the duration of these marketable securities, the more susceptible they are to changes in market interest rates and bond yields. As interest rates increase, those marketable securities purchased at a lower yield show a mark-to-market unrealized loss. The unrealized losses are due primarily to changes in credit spreads and interest rates. We expect to realize the full value of these investments upon maturity or sale.

As of September 30, 2017, the contractual maturities of our investments did not exceed 24 months. The fair values of available-for-sale investments, by remaining contractual maturity, are as follows (in thousands):



	September 30, 2017
Due in 1 year or less	$	300,957
Due in 1 year through 2 years	187,678
Total marketable securities	$	488,635

The weighted average remaining duration of our current marketable securities is approximately 0.8 years as of September 30, 2017. As we view these securities as available to support current operations, we classify securities with maturities beyond 12 months as current assets under the caption marketable securities in the accompanying unaudited condensed consolidated balance sheets.

Accounts Receivable, net

Accounts receivable, net consists of the following (in thousands):



	September 30, 2017			December 31, 2016
Accounts receivable	$	220,106		$	254,640
Allowance for doubtful accounts	(81		)	(204		)
Sales return reserve	(7,414		)	(1,317		)
Accounts receivable, net	$	212,611		$	253,119

Inventories

Inventories consist of the following (in thousands):



	September 30, 2017		December 31, 2016
Raw materials	$	99,640	$	99,190
Finished goods	233,517		137,300
Total inventories	$	333,157	$	236,490

Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consist of the following (in thousands):



	September 30, 2017		December 31, 2016
Inventory deposit	$	31,957	$	60,315
Prepaid income taxes	14,583		17,383
Other current assets	126,190		79,140
Other prepaid expenses and deposits	13,927		11,846
Total prepaid expenses and other current assets	$	186,657	$	168,684

Property and Equipment, net

Property and equipment, net consists of the following (in thousands):



	September 30, 2017			December 31, 2016
Equipment and machinery	$	46,550		$	40,721
Computer hardware and software	21,527			17,420
Furniture and fixtures	2,993			2,879
Leasehold improvements	30,491			29,498
Building	35,154			35,154
Construction-in-process	135			421
Property and equipment, gross	136,850			126,093
Less: accumulated depreciation	(63,789		)	(49,132		)
Property and equipment, net	$	73,061		$	76,961

Depreciation and amortization expense was $5.2 million and $5.1 million, for the three months ended September 30, 2017 and 2016, respectively, and $15.0 million and $14.8 million for the nine months ended September 30, 2017 and 2016, respectively.

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):



	September 30, 2017		December 31, 2016
Accrued compensation costs	$	44,477	$	52,854
Accrued warranty costs	8,286		6,744
Accrued manufacturing costs	25,592		14,824
Accrued professional fees	6,666		6,829
Accrued taxes	1,315		1,098
Other	8,123		8,602
Total accrued liabilities	$	94,459	$	90,951

Warranty Accrual

We offer a one-year warranty on all of our hardware products and a 90-day warranty against defects in the software embedded in the products. The accrued warranty liability is recorded in accrued liabilities in the accompanying unaudited condensed consolidated balance sheets.

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



	Nine Months Ended September 30,
	2017			2016
Warranty accrual, beginning of period	$	6,744		$	4,718
Liabilities accrued for warranties issued during the period	5,020			3,420
Warranty costs incurred during the period	(3,478		)	(2,541		)
Warranty accrual, end of period	$	8,286		$	5,597