Income Taxes (Tax Return Reported Federal Net Operating Losses and Tax Credits) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Federal [Member]
Net operating losses	$ 402,192
Net operating losses carried forward, expiration date	Dec. 31, 2034
Foreign [Member]
Net operating losses	29,705
Research Tax Credit [Member]
Tax credit	10,975
Tax credit carryforwards, expiration date	Dec. 31, 2034
Alternative Minimum Tax [Member]
Tax credit	$ 94

Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

Name:	us-gaap_OperatingLossCarryforwards
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Expiration date of each operating loss carryforward included in operating loss carryforward, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_OperatingLossCarryforwardsExpirationDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Carryforwards

-URI http://asc.fasb.org/extlink&oid=6506874

+ Details

Name:	us-gaap_TaxCreditCarryforwardAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Expiration date of the tax credit carryforward, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_TaxCreditCarryforwardExpirationDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=us-gaap_DomesticCountryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=us-gaap_ForeignCountryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TaxCreditCarryforwardAxis=nvax_AlternativeMinimumTaxMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TaxCreditCarryforwardAxis=us-gaap_ResearchMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: