Restructuring - Summary of Restructuring Liability (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Restructuring Reserve [Roll Forward]
Balance at December 31, 2013	$ 881us-gaap_RestructuringReserve
Accruals	7,760nvtl_AdditionsToRestructuringReserve
Payments	(5,360)us-gaap_PaymentsForRestructuring
Share-based compensation	(1,298)
Balance at December 31, 2014	1,983us-gaap_RestructuringReserve
Facility Exit Related Costs
Restructuring Reserve [Roll Forward]
Balance at December 31, 2013	881
Accruals	1,170
Payments	(1,819)
2013 Initiatives \| Employment Contract Costs
Restructuring Reserve [Roll Forward]
Balance at December 31, 2013	0
Accruals	1,713
Payments	(1,713)
Share-based compensation	0
Balance at December 31, 2014	0
2013 Initiatives \| Facility Exit Related Costs
Restructuring Reserve [Roll Forward]
Share-based compensation	0
Balance at December 31, 2014	232
2014 Initiatives \| Employment Contract Costs
Restructuring Reserve [Roll Forward]
Balance at December 31, 2013	0
Accruals	3,579
Payments	(1,828)
Share-based compensation	0
Balance at December 31, 2014	1,751
2014 Initiatives \| Share-based Compensation Costs
Restructuring Reserve [Roll Forward]
Balance at December 31, 2013	0
Accruals	1,298
Payments	0
Share-based compensation	(1,298)
Balance at December 31, 2014	$ 0

Additions during the period to the restructuring reserve.

No definition available.

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- Definition

Restructuring Charges For Shared Based Compensation Acceleration For Termination Of Chief Executive Officer

+ References

No definition available.

+ Details

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- Definition

Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

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- Definition

Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 5.P.4(b))

-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section P

-Subsection 3, 4

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