Represents the initial term for research under collaborative arrangements.

No definition available.

Name:	snta_CollaborativeArrangementInitialTermForResearch
Namespace Prefix:	snta_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the license revenue recognized during the period under the collaborative agreement.

No definition available.

Name:	snta_CollaborativeArrangementLicenseRevenueRecognized
Namespace Prefix:	snta_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the accelerated recognition of remaining deferred revenue from upfront payment during the period under the collaborative agreement.

No definition available.

Name:	snta_CollaborativeArrangementNonRefundableUpfrontLicenseFeeAcceleratedRecognition
Namespace Prefix:	snta_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the amount received in research and development support.

No definition available.

Name:	snta_CollaborativeArrangementResearchAndDevelopmentSupportReceived
Namespace Prefix:	snta_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the non-refundable upfront license payment received.

No definition available.

Name:	snta_CollaborativeArrangementUpfrontLicenseFeeReceived
Namespace Prefix:	snta_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Name:	us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

License and Development Agreements (Details) (Roche Agreement, Roche, USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended			9 Months Ended		24 Months Ended
	Jan. 31, 2009	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2010
Roche Agreement \| Roche
License and Development Agreements
Upfront license fee received	$ 16
Initial term for research	2 years
Amount received related to research and development support							21.2
Accelerated recognition of remaining deferred revenue from upfront payment			2.1
License revenue recognized		$ 0		$ 1.1	$ 0	$ 3.4