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SHARE-BASED COMPENSATION - Narrative (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 17, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Grant date fair value of options granted (in dollars per share) $ 29.92us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 28.27us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 17.66us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue  
Tax benefit recognized from compensation expense $ 3,200,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense      
Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unrecognized compensation cost related to stock options 3,200,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
     
Weighted average period for recognition of compensation consts 1 year 8 months 12 days      
Total compensation expense recognized 2,300,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
2,200,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
1,300,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
 
Tax benefit recognized from compensation expense 900,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
800,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
300,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
 
Time-based Shares [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average period for recognition of compensation consts 1 year 10 months 24 days      
Unrecognized compensation cost with respect to restricted stock 4,200,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
/ us-gaap_AwardTypeAxis
= ntks_TimeBasedSharesMember
     
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Total compensation expense recognized 3,900,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
8,300,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
3,300,000us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
 
Tax benefit recognized from compensation expense 1,500,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
3,200,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
1,300,000us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
 
Aggregate fair value of shares vested 4,800,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
12,100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
4,600,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
 
Performance Shares [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average period for recognition of compensation consts 1 year 10 months 24 days      
Unrecognized compensation cost with respect to restricted stock probable to vest 2,700,000ntks_EmployeeServiceSharebasedCompensationNonvestedAwardsProbableofVestingCompensationNotyetRecognizedSharebasedAwardsOtherthanOptions
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
     
Unrecognized compensation cost with respect to restricted stock not probable to vest 9,500,000ntks_EmployeeServiceSharebasedCompensationNonvestedAwardsNotProbableofVestingCompensationNotyetRecognizedSharebasedAwardsOtherthanOptions
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
     
Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Forfeiture rate 0.00%ntks_SharebasedCompensationForfeitureRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
     
Minimum [Member] | Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years) 3 years      
Minimum [Member] | Time-based Shares [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years) 3 years      
Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Forfeiture rate 26.00%ntks_SharebasedCompensationForfeitureRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
     
Maximum [Member] | Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years) 5 years      
Maximum [Member] | Time-based Shares [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period (in years) 5 years      
Omnibus Incentive Plan 2009 [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares authorized for grant (in shares)       2,885,907us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= ntks_OmnibusIncentivePlan2009Member
Annual authorized cash award per participant, maximum       $ 5,000,000ntks_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualAuthorizedCashAwardPerParticipantMaximum
/ us-gaap_PlanNameAxis
= ntks_OmnibusIncentivePlan2009Member
Number of shares available for grant (in shares) 1,148,218us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= ntks_OmnibusIncentivePlan2009Member
     
Omnibus Incentive Plan 2009 [Member] | Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares authorized for grant (in shares)       1,076,555us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= ntks_OmnibusIncentivePlan2009Member
Number of shares authorized per participant annually (in shares)       627,990ntks_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedPerParticipantAnnually
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= ntks_OmnibusIncentivePlan2009Member
Omnibus Incentive Plan 2009 [Member] | Share Awards Other than Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares authorized per participant annually (in shares)       627,990ntks_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorizedPerParticipantAnnually
/ us-gaap_AwardTypeAxis
= ntks_ShareAwardsOtherThanStockOptionsMember
/ us-gaap_PlanNameAxis
= ntks_OmnibusIncentivePlan2009Member