At June 30, 2020 and December 31, 2019, a total of $32.8 million and $11.9 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, term deposit and certificate of deposit. The amortized cost, gross unrealized holding gains or losses, and fair value of the Company’s investments by major investments type are summarized in the tables below (in thousands):

	June 30, 2020
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
U.S. treasury notes and bills	$	225,117	$	1,062	$	—		$	226,179
Certificates of deposit		30,000		138		—			30,138
Equity investments		125		104		—			229
Total investments	$	255,242	$	1,304	$	—		$	256,546

	December 31, 2019
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
U.S. treasury notes and bills	$	426,995	$	536	$	(25	)	$	427,506
Certificates of deposit		30,000		32		—			30,032
Bond and mutual funds		10,730		86		—			10,816
Equity investments		125		130		—			255
Total investments	$	467,850	$	784	$	(25	)	$	468,609

At June 30, 2020, all of the available-for-sale investments had contractual maturities within one year. During the three and six months ended June 30, 2020 and 2019, the Company did not recognize any other-than-temporary impairment loss.

	June 30, 2020		December 31, 2019
Raw materials	$	327	$	325
Work-in-progress		3,815		2,264
Finished goods		4,440		4,298
Total inventories	$	8,582	$	6,887

The provision to write-down excess and obsolete inventory was immaterial for the three and six months ended June 30, 2020.

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

	June 30, 2020		December 31, 2019
Unbilled contract assets	$	—	$	180,000
Deferred revenues from associated contracts		—		(54,790	)
Net unbilled contract assets		—		125,210
Prepaid assets		4,429		6,464
Other current assets		2,052		1,717
Total prepaid expenses and other current assets	$	6,481	$	133,391

The unbilled contract assets as of December 31, 2019 included two regulatory milestones totaling $130.0 million under the Europe Agreement with Astellas associated with the planned MAA submission in Europe. The MAA was submitted in the second quarter of 2020. Therefore the $130 million milestones were billed in the same quarter. The unbilled contract assets as of December 31, 2019 also included a $50.0 million regulatory milestone under the U.S./RoW Agreement with AstraZeneca associated with the NDA submission in the U.S, which was submitted in December 2019 and accepted for review in February 2020. Therefore, the $50.0 million milestone was billed during the first quarter of 2020. See Note 2 for details.

	June 30, 2020			December 31, 2019
Leasehold improvements	$	100,159		$	101,548
Laboratory equipment		17,362			17,329
Machinery		7,660			8,217
Computer equipment		8,930			8,399
Furniture and fixtures		5,873			5,822
Construction in progress		1,225			1,792
Total property and equipment	$	141,209		$	143,107
Less: accumulated depreciation		(104,225	)		(100,364	)
Property and equipment, net	$	36,984		$	42,743

	June 30, 2020		December 31, 2019
Preclinical and clinical trial accruals	$	21,691	$	16,279
API product price adjustment		—		36,324
Payroll and related accruals		14,266		19,784
Property taxes and other		1,145		2,044
Professional services		5,653		4,842
Other		7,709		4,543
Total accrued liabilities	$	50,464	$	83,816

The amount of $36.3 million accrued as of December 31, 2019 was related to the change in estimated variable consideration of API product at the time the roxadustat listed price was issued by the Japanese Ministry of Health, Labour and Welfare. The amount was fully paid during the first quarter of 2020.

	June 30, 2020		December 31, 2019
Accrued long-term co-promotional expenses	$	116,230	$	53,071
Other long-term tax liabilities		8,653		8,913
Operating lease liabilities, non-current		572		942
Other		1,787		1,340
Total other long-term liabilities	$	127,242	$	64,266

The accrued long-term co-promotional expenses of $116.2 million and $53.1 million as of June 30, 2020 and December 31, 2019, respectively, were related to the estimated amount payable to AstraZeneca for its sales and marketing efforts associated with the commercial launch and sales for roxadustat in China. The payment for such amount is not expected to occur within the next year. On July 8, 2020, the Parties into an amendment to the China Agreement, relating to the development and commercialization of roxadustat in China. As a result, such accrued long-term co-promotional expenses will be reduced by approximately $82 million in the third quarter of 2020. See Note 10 for details.