CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2018
Statement of Stockholders' Equity [Abstract]
Issuance of common stock and common stock warrants, issuance costs	$ 2,193	$ 4,070	$ 959

Stock Issued During Period, New Issues, Issuance Costs

No definition available.

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Namespace Prefix:	sesn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration