Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities
Net income (loss)	$ 1,874,325	$ (40,256)
Less: Net Income from discontinued operations	1,965,202	43,838
Net loss from continuing operations	(90,877)	(84,094)
Adjustments to reconcile net loss from continuing operations to net cash used in operating activities:
Depreciation and amortization	2,479	2,474
Stock-based compensation expense	14,854	15,670
Net amortization of premium (accretion of discount) on marketable securities	1,664	126
Non-cash operating lease expense	2,417	2,203
Changes in operating assets and liabilities:
Prepaid expenses and other current and non-current assets	(3,621)	(1,076)
Accounts payable	(2,941)	(883)
Accrued expenses and other current liabilities	(12,697)	(10,972)
Operating lease liabilities	(1,504)	(2,229)
Net cash used in operating activities - continuing operations	(90,226)	(78,781)
Net cash used in operating activities - discontinued operations	(30,523)	(26,577)
Net cash used in operating activities	(120,749)	(105,358)
Investing activities
Purchases of marketable securities	(61,863)	(54,911)
Proceeds from maturities and sales of marketable securities	134,016	167,501
Purchases of property and equipment	(1,012)	(4,196)
Net cash provided by investing activities - continuing operations	71,141	108,394
Net cash provided by (used in) investing activities - discontinued operations	1,802,936	(259)
Net cash provided by investing activities	1,874,077	108,135
Financing activities
Payments on financing lease obligations	(86)	(80)
Net proceeds from stock option exercises and employee stock purchase plan	7,347	5,465
Net cash provided by financing activities - continuing operations	7,261	5,385
Net cash provided by financing activities - discontinued operations	0	0
Net cash provided by financing activities	7,261	5,385
Net change in cash and cash equivalents	1,760,589	8,162
Cash and cash equivalents at beginning of the period	127,436	80,931
Cash and cash equivalents at end of the period	1,888,025	89,093
Supplemental disclosure of non-cash investing and financing transactions
Additions to property and equipment in accounts payable and accrued expenses	6	5,444
Operating lease liabilities arising from obtaining operating lease assets	$ 0	$ 0