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Stock-Based Compensation - Stock incentive plan and other information (Details) - USD ($)		3 Months Ended		6 Months Ended
	Mar. 20, 2007	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 17, 2020	Nov. 02, 2010
Share-based Compensation Arrangement by Share-based Payment Award
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options		$ 483,000		$ 483,000
General and Administrative Expenses and Research and Development Expense [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense		34,000,000	$ 40,000,000	67,000,000	$ 79,000,000
Research and Development Expense \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense		16,000,000	15,000,000	31,000,000	31,000,000
Consultant [Member] \| General and Administrative Expenses and Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense		49,000	27,000	98,000	53,000
Consultant [Member] \| Research and Development Expense
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense		$ 3,000,000	$ 4,000,000	$ 7,000,000	$ 6,000,000
2007 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	71,429	5,145		5,145
2007 Stock Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	7,143
2010 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number		1,540,000		1,540,000			85,714
2010 Stock Plan [Member] \| Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number		2,452,273		2,452,273
2020 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number						4,000,000