Balance Sheet Components

12 Months Ended

Dec. 31, 2019

Balance Sheet Related Disclosures [Abstract]

Inventories

Inventories consist of the following (in thousands):



	December 31,
	2019		2018
Raw materials	$	54,947	$	26,119
Work in process	30,974		13,784
Finished goods	26,130		15,738
Total inventories	$	112,051	$	55,641

Prepaid Expenses and Other Current Assets

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



	December 31,
	2019		2018
Tax related receivables	$	41,252	$	36,794
Current promissory note ¹	25,005		—
Other prepaid expenses and current assets	24,637		23,227
Prepaid software and maintenance	7,128		5,938
Other current receivables	4,428		6,511
Total prepaid expenses and other current assets	$	102,450	$	72,470


¹	Refer to Note 5“Equity Method Investments” of the Notes to Consolidated Financial Statements for more information.

Property, Plant and Equipment, Net

Property, plant and equipment consist of the following (in thousands):



		December 31,
	Generally Used Estimated Useful Life	2019			2018
Clinical and manufacturing equipment	Up to 10 years	$	309,809		$	236,179
Building	20 years	209,643			139,315
Computer software	3 years	61,722			59,617
Leasehold improvements	Lease term ¹	53,327			77,168
Furniture and fixtures	5 years	44,373			33,436
Computer hardware	3 years	39,199			34,297
Land	—	26,422			17,630
CIP	—	116,751			95,414
Total		861,246			693,056
Less: Accumulated depreciation and amortization and impairment charges		(229,516		)	(171,727		)
Total property, plant and equipment, net		$	631,730		$	521,329


¹	Shorter of the remaining lease term or the estimated useful lives of the assets.

Depreciation and amortization was $79.0 million, $54.7 million and $37.7 million for the year ended December 31, 2019, 2018 and 2017, respectively. In the first quarter of 2019, we recorded impairment losses of $14.3 million related to leasehold improvements and other fixed assets. Refer to Note 8“Impairments and Other (Gains) Charges” of the Notes to Consolidated Financial Statements for more information.

On September 26, 2019, we entered into a Purchase and Sale Agreement to purchase a building located in San Jose, California for $21.3 million. The remaining and substantial portion of the purchase price will be paid on or before the closing date, which is expected to occur in the first quarter of 2020.

Accrued Liabilities

Accrued liabilities consist of the following (in thousands):



	December 31,
	2019		2018
Accrued payroll and benefits	$	162,486	$	127,109
Accrued expenses	55,529		39,323
Current operating lease liabilities	15,737		—
Accrued income taxes	14,130		5,752
Accrued sales rebate	11,393		5,668
Others	60,683		56,827
Total accrued liabilities	$	319,958	$	234,679

Warranty

We regularly review the balance for accrued warranty and update based on historical warranty trends. Actual warranty costs incurred have not materially differed from those accrued; however, future actual warranty costs could differ from the estimated amounts.

Warranty accrual as of December 31, 2019 and 2018 consists of the following activity (in thousands):



Accrued warranty as of December 31, 2017	$	5,929
Charged to cost of net revenues	15,059
Actual warranty expenditures	(12,437		)
Accrued warranty as of December 31, 2018	8,551
Charged to cost of net revenues	12,421
Actual warranty expenditures	(9,767		)
Accrued warranty as of December 31, 2019	$	11,205

Deferred Revenues

Deferred revenues consist of the following (in thousands):



	December 31,
	2019		2018
Deferred revenues - current	$	563,762	$	393,138
Deferred revenues - long-term ¹	35,503		17,051


¹	Included in other long-term liabilities within our Consolidated Balance Sheet

During the year ended December 31, 2019 and 2018, we recognized $2.4 billion and $2.0 billion of net revenues, respectively, of which $262.7 million and $180.6 million was included in the deferred revenues balance at December 31, 2018 and December 31, 2017, respectively.