Financial Statement Details (in millions)

Short-Term Marketable Securities, Available-for-Sale

Short-term marketable securities, consisting solely of debt securities were as follows:



	December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Market Value
U.S. government agencies	$	87.5	$	—	$	(0.2	)	$	87.3
Commercial paper	14.7		—		—			14.7
Corporate debt	5.1		—		—			5.1
Total	$	107.3	$	—	$	(0.2	)	$	107.1



	December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Market Value
U.S. government agencies	$	22.2	$	—	$	—	$	22.2
Corporate debt	3.8		—		—		3.8
Commercial paper	3.2		—		—		3.2
Total	$	29.2	$	—	$	—	$	29.2

As of December 31, 2017, the estimated market value of available-for-sale marketable securities with contractual maturities of up to one year and up to 16 months were $92.7 million and $14.4 million, respectively.

Accounts Receivable



	December 31,
	2017			2016
Accounts receivable	$	145.8		$	114.3
Less allowance for doubtful accounts, sales returns and discounts	(11.5		)	(12.6		)
Total	$	134.3		$	101.7

Inventory



	December 31,
	2017		2016
Raw materials	$	20.0	$	20.1
Work-in-process	8.2		2.3
Finished goods	17.0		23.0
Total	$	45.2	$	45.4

During 2016, we recorded charges of $3.5 million in cost of goods sold related to excess and obsolete receiver inventory primarily related to the February 23, 2016 customer notification regarding the audible alarms and alerts associated with our receivers which was classified as a voluntary Class 1 recall by the FDA and was closed as of August 11, 2017.

Property and Equipment



	December 31,
	2017			2016
Building ⁽¹⁾	$	6.0		$	6.0
Furniture and fixtures	5.7			5.8
Computer equipment	25.6			22.7
Machinery and equipment	33.8			31.4
Leasehold improvements	41.7			25.6
Construction in progress ⁽²⁾	87.6			65.1
Total	200.4			156.6
Accumulated depreciation	(54.8		)	(47.2		)
Property and equipment, net	$	145.6		$	109.4

⁽¹⁾ As described in Footnote 5 “Commitments and Contingencies,” although we do not legally own these premises, we were deemed the owner of the construction project during the construction period of our new manufacturing facility in Mesa, Arizona under a build-to suit lease arrangement.

⁽²⁾ Construction in progress as of December 31, 2017 and December 31, 2016 include approximately $33.6 million and $24.8 million, respectively, related to our new manufacturing facility in Mesa, Arizona with the remaining balance as of December 31, 2017 and December 31, 2016 primarily related to machinery and equipment.

Depreciation expense related to property and equipment for the twelve months ended December 31, 2017, 2016, and 2015 was $16.1 million, $14.4 million, and $10.2 million, respectively.

During 2017 we recorded a $9.2 million loss on disposal of machinery and equipment, the majority of which was previously contained within the construction in progress balance. The loss on disposal was recorded in operating expense, primarily within the "Research and development" line item on our Consolidated Statements of Operations and was associated with changes in our product portfolio.

Accounts Payable and Accrued Liabilities



	December 31,
	2017		2016
Accounts payable trade⁽¹⁾	$	46.7	$	41.1
Accrued tax, audit, and legal fees	7.1		4.5
Accrued rebates	13.9		8.2
Accrued warranty	8.8		9.8
Accrued other⁽¹⁾	10.7		4.5
Total	$	87.2	$	68.1

⁽¹⁾ December 31, 2016 amounts have been modified for comparative reporting purposes.

Accrued Payroll and Related Expenses



	December 31,
	2017		2016
Accrued paid time off	$	7.9	$	6.4
Accrued wages, bonus and taxes	37.6		24.5
Other accrued employee benefits	3.0		2.5
Total	$	48.5	$	33.4

Accrued Warranty

Warranty costs are reflected in the consolidated statements of operations as cost of sales. A reconciliation of our accrued warranty costs for the twelve months ended December 31, 2017 and 2016 were as follows:



	Years Ended December 31,
	2017			2016
Beginning balance	$	9.8		$	3.3
Charges to costs and expenses	18.4			25.0
Costs incurred	(19.4		)	(18.5		)
Ending balance	$	8.8		$	9.8

Other Liabilities



	December 31, 2017		December 31, 2016
Financing lease obligations	$	6.7	$	6.7
Deferred rent	8.7		7.3
Other	2.8		2.6
Total	$	18.2	$	16.6