Employee Benefits (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Maximum contribution percentage of compensation	100.00%
Contributions to employee benefits plan	$ 1.5	$ 1.5	$ 0.8
Contributions and other expenses related to foreign subsidiary	$ 0.5	$ 0.5	$ 0.5
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	4.00%
Next 2% Of Participants Deferral [Member]
Employer match percentage	50.00%
Percentage of employee deferral eligible for employer matching contribution	2.00%
First 3% Of Participants Deferral [Member]
Employer match percentage	100.00%
Percentage of employee deferral eligible for employer matching contribution	3.00%

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

Amount of cost for defined contribution plan.

+ 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=49170846&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

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
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

- Details

Name:	us-gaap_CollectiveBargainingArrangementAxis=nvax_NextTwoPercentOfParticipantsDeferralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CollectiveBargainingArrangementAxis=nvax_FirstThreePercentOfParticipantsDeferralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: