Goodwill And Intangible Assets, Net (Schedule Of Change In Carrying Values Of Goodwill Assets By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Gross goodwill, beginning balance	$ 752,497	$ 750,674
Acquisitions		10,179
Adjustments	2,659	(200)
Foreign currency translation	691	(8,156)
Gross goodwill, ending balance	755,847	752,497
Accumulated goodwill impairment	(122,045)	(122,045)
Accumulated amortization	(5,425)	(5,425)
Net goodwill	628,377	625,027
Healthcare [Member]
Goodwill [Line Items]
Gross goodwill, beginning balance	272,032	264,163
Acquisitions		8,057
Adjustments	(43)	(12)
Foreign currency translation	34	(176)
Gross goodwill, ending balance	272,023	272,032
Net goodwill	272,023	272,032
Energy [Member]
Goodwill [Line Items]
Gross goodwill, beginning balance	77,924	76,566
Acquisitions		2,122
Adjustments	2,749
Foreign currency translation	102	(764)
Gross goodwill, ending balance	80,775	77,924
Net goodwill	80,775	77,924
Financial Services Advisory and Compliance [Member]
Goodwill [Line Items]
Gross goodwill, beginning balance	53,784	55,341
Acquisitions
Adjustments	(9)	(35)
Foreign currency translation	93	(1,522)
Gross goodwill, ending balance	53,868	53,784
Net goodwill	53,868	53,784
Disputes, Forensics & Legal Technology [Member]
Goodwill [Line Items]
Gross goodwill, beginning balance	348,757	354,604
Acquisitions
Adjustments	(38)	(153)
Foreign currency translation	462	(5,694)
Gross goodwill, ending balance	349,181	348,757
Accumulated goodwill impairment	(122,045)	(122,045)
Accumulated amortization	(5,425)	(5,425)
Net goodwill	$ 221,711	$ 221,287

Goodwill, accumulated amortization

No definition available.

Name:	nci_GoodwillAccumulatedAmortization
Namespace Prefix:	nci_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=64834752&loc=SL49117168-202975

+ Details

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

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

+ Details

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

- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

+ Details

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

- Definition

Amount before accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

+ Details

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

- Definition

Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

+ Details

Name:	us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_GoodwillLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease), classified as other, of an asset representing the future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

+ Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=nci_HealthcareMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=nci_EnergyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=nci_FinancialServicesAdvisoryAndComplianceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=nci_DisputesForensicsAndLegalTechnologyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: