Employee Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Maximum contribution percentage of compensation	100.00%
Employer match percentage		50.00%	25.00%
Percentage of employee deferral eligible for employer matching contribution	6.00%
Contributions to employee benefits plan	$ 0.5	$ 0.4	$ 0.1
Contributions and other expenses related to foreign subsidiary	$ 0.4	$ 0.2

The amount of the cost recognized during the period for defined contribution plans and other expenses.

No definition available.

Name:	nvax_DefinedContributionPlanCostAndOtherExpenses
Namespace Prefix:	nvax_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the percentage of the participant's deferral that is eligible for an employer matching contribution.

+ References

No definition available.

+ Details

Name:	nvax_DefinedContributionPlanPercentOfEmployeeDeferralEligibleForEmployerMatching
Namespace Prefix:	nvax_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration