Consolidated Statements of Cash Flows (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Statement of Cash Flows [Abstract]
Future royalties transaction costs	$ 4.4nktr_PaymentForTransactionCosts
Senior secured notes issuance costs	$ 4.5us-gaap_PaymentsOfDebtIssuanceCosts

The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585

Name:	us-gaap_PaymentsOfDebtIssuanceCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration