At September 30, 2019 and December 31, 2018, a total of $18.1 million and $21.9 million, respectively, of the Company’s cash and cash equivalents were held outside of the U.S. in its foreign subsidiaries to be used primarily for its China operations.

The Company’s investments consist of available-for-sale debt investments, marketable equity investments, a term deposit and a certificate of deposit. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s available-for-sale investments by major investments type are summarized in the tables below (in thousands):

	September 30, 2019
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
US treasury notes and bills	$	401,377	$	688	$	(25	)	$	402,040
Certificates of deposit		30,000		—		—			30,000
Bond and mutual funds		10,668		80		—			10,748
Equity investments		125		126		—			251
Total investments	$	442,170	$	894	$	(25	)	$	443,039

	December 31, 2018
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
US treasury notes and bills	$	467,296	$	109	$	(69	)	$	467,336
Term deposit		80,000		—		—			80,000
Certificates of deposit		30,000		—		(90	)		29,910
Bond and mutual funds		10,464		20		—			10,484
Equity investments		125		109		—			234
Total investments	$	587,885	$	238	$	(159	)	$	587,964

At September 30, 2019, all of the available-for-sale investments had contractual maturities within one year. The Company periodically reviews its available-for-sale investments and term deposit for other-than-temporary impairment. The Company considers factors such as the duration, severity and the reason for the decline in value, the potential recovery period and its intent to sell. For debt securities, the Company also considers whether (i) it is more likely than not that the Company will be required to sell the debt securities before recovery of their amortized cost basis, and (ii) the amortized cost basis cannot be recovered as a result of credit losses. During the three and nine months ended September 30, 2019 and 2018, the Company did not recognize any other-than-temporary impairment loss.

The Company started capitalizing inventory costs in June 2019 when FibroGen China began productions of roxadustat for commercial sales purposes. There was no provision to write-down excess and obsolete inventory for the three and nine months ended September 30, 2019.

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

	September 30, 2019			December 31, 2018
Unbilled contract assets	$	180,000		$	—
Deferred revenues from associated contracts		(53,988	)		—
Net unbilled contract assets		126,012			—
Prepaid assets		4,051			2,705
Other current assets		3,652			2,224
Total prepaid expenses and other current assets	$	133,715		$	4,929

The unbilled contract assets as of September 30, 2019 were related to two regulatory milestones totaling $130.0 million under the Europe Agreement with Astellas associated with the planned MAA submission in Europe, and a $50.0 million regulatory milestone under the U.S./RoW Agreement with AstraZeneca associated with the planned NDA submission in the U.S. See Note 2 for details.

	September 30, 2019			December 31, 2018
Leasehold improvements	$	101,339		$	101,200
Building shell		—			53,880
Laboratory equipment		16,932			16,405
Machinery		8,691			8,382
Computer equipment		7,227			6,473
Furniture and fixtures		5,789			5,690
Construction in progress		2,332			367
Total property and equipment	$	142,310		$	192,397
Less: accumulated depreciation		(99,102	)		(65,199	)
Property and equipment, net	$	43,208		$	127,198

As of December 31, 2018, the Company had $53.9 million building shell cost and $13.5 million accumulated depreciation related to its building leases under build-to-suit arrangements. Upon the adoption of ASC 842 as of January 1, 2019, using the modified retrospective transition method, the Company derecognized these assets previously recognized under ASC 840 build-to-suit designation. Up to December 31, 2018, the leasehold improvements related to these building leases were depreciated over the life of the building under ASC 840. Upon the adoption of ASC 842, these leasehold improvements should have a useful life based on the lease term. As a result, at the adoption date, the Company recorded a cumulative adjustment of $38.9 million to the accumulated depreciation for these leasehold improvements so that their net balance equals the undepreciated amount had the useful life of the leasehold improvements always been equal to the lease terms. Refer to Note 1 for details.

	September 30, 2019		December 31, 2018
Preclinical and clinical trial accruals	$	41,546	$	35,413
Payroll and related accruals		17,604		21,430
Property taxes and other		2,389		1,095
Professional services		4,063		2,648
Other		5,223		5,537
Total accrued liabilities	$	70,825	$	66,123