Consolidated Balance Sheets - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 360,487,000	$ 65,376,000
Short-term investments	53,988,000	53,325,000
Prepaid expenses and other current assets	5,542,000	1,289,000
Total current assets	420,017,000	119,990,000
Long-term Investments	44,770,000
Property and equipment, net	15,954,000	1,847,000
Operating lease assets	17,356,000	2,225,000
Restricted cash	408,000	312,000
Other assets	2,910,000	451,000
Total assets	501,415,000	124,825,000
Current liabilities:
Accounts payable	4,677,000	878,000
Accrued expenses and other current liabilities	21,419,000	11,925,000
Operating lease liabilities	285,000	877,000
Total current liabilities	26,381,000	13,680,000
Operating lease liabilities, net of current portion	18,506,000	2,109,000
Preferred stock purchase right liability		1,615,000
Total liabilities	44,887,000	17,404,000
Commitments and contingencies (Note 12)
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 80,000,000 shares and no shares authorized as of December 31, 2021 and 2020, respectively; no shares issued and outstanding as of December 31, 2021 and 2020
Common stock, $0.0001 par value; 800,000,000 and 147,027,681 shares authorized as of December 31, 2021 and 2020, respectively; 121,382,547 and 25,189,673 shares issued at December 31, 2021 and 2020, respectively; 119,102,505 and 21,923,173 shares outstanding at December 31, 2021 and 2020, respectively	12,000	3,000
Additional paid-in capital	694,844,000	1,413,000
Accumulated other comprehensive (loss) income	(162,000)	2,000
Accumulated deficit	(238,166,000)	(115,402,000)
Total stockholders' equity (deficit)	456,528,000	(113,984,000)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 501,415,000	124,825,000
Convertible Preferred Stock
Current liabilities:
Convertible preferred stock (Series A, B-1 and B-2), $0.0001 par value; no shares and 97,622,409 shares authorized as of December 31, 2021 and 2020, respectively; no shares and 69,584,682 shares issued and outstanding as of December 31, 2021 and 2020, respectively; aggregate liquidation preference of $0 and $230,924 as of December 31, 2021 and 2020, respectively		$ 221,405,000

Preferred stock purchase right liability.

No definition available.

Name:	eras_PreferredStockPurchaseRightLiability
Namespace Prefix:	eras_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).