Name:	navg_Companys401KEmployerMatchExpense
Namespace Prefix:	navg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents the maximum percentage of total pay the Company matches employee contributions to the plan of total pay for the Company's Retirement Savings Plan.

No definition available.

Name:	navg_DefinedBenefitPlanEmployerContributionPercentage
Namespace Prefix:	navg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the percentage of total pay the Company matches employee contributions to the plan of total pay for the Company's Retirement Savings Plan, subject to the Company's discretion.

No definition available.

Name:	navg_DefinedBenefitPlanEmployerDiscretionaryMatchPercentage
Namespace Prefix:	navg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage at which employees vest into the Defined Benefit Plan, subsequent years.

No definition available.

Name:	navg_DefinedContributionPlanAdditionalEmployeeVestingPercentage
Namespace Prefix:	navg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage at which employees vest into the Defined Benefit Plan.

No definition available.

Name:	navg_DefinedContributionPlanEmployeeVestingPercentage
Namespace Prefix:	navg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Defined Contribution Plan Vesting Period

No definition available.

Name:	navg_DefinedContributionPlanVestingPeriod
Namespace Prefix:	navg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	navg_EmployeeBenefitsDisclosureLineItems
Namespace Prefix:	navg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Employer 401(k) Matching Contribution to Employee, Maximum

No definition available.

Name:	navg_Employer401KMatchingContributionToEmployeeMaximum
Namespace Prefix:	navg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Amount of bonus eligible for contribution into the employee defined benefit plan.

No definition available.

Name:	navg_GrossEligiblePayBonus
Namespace Prefix:	navg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents the maximum percentage of total pay the Company matches employee contributions to the plan of total pay for the Company's Retirement Savings Plan, subject to the Internal Revenue Code.

No definition available.

Name:	navg_MaximumEmployeeEarningsContributionFor401K
Namespace Prefix:	navg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: 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