Annual report pursuant to Section 13 and 15(d)

Deferred Compensation Plan - Additional Information (Detail)

v2.4.1.9
Deferred Compensation Plan - Additional Information (Detail) (USD $)
12 Months Ended 6 Months Ended 12 Months Ended
Dec. 31, 2014
Dec. 31, 2014
Jun. 29, 2014
Dec. 31, 2013
Dec. 31, 2012
Investments And Employee Deferred Compensation Plan [Line Items]          
Percentage of deferred salary and commissions 25.00%hlm_DeferredCompensationPlanMaximumPercentageDeferredOfAnnualBaseSalary        
Percentage of bonuses 100.00%hlm_DeferredCompensationPlanMaximumPercentageDeferredOfAnnualBonus        
Percentage of deferred matching contribution amount 25.00%hlm_DeferredCompensationArrangementMatchingContributionPercentage        
Vesting schedule 5 years        
Successor [Member]          
Investments And Employee Deferred Compensation Plan [Line Items]          
Assets held in mutual funds 2,244,000us-gaap_RestrictedInvestments
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
$ 2,244,000us-gaap_RestrictedInvestments
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
     
Restricted investments 494,000us-gaap_RestrictedInvestmentsCurrent
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
494,000us-gaap_RestrictedInvestmentsCurrent
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
     
Trading gains and offsetting compensation expense   43,000us-gaap_UnrealizedGainLossOnSecurities
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
     
Distributions from the deferred compensation plan aggregated 0us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
0us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
     
Predecessor [Member]          
Investments And Employee Deferred Compensation Plan [Line Items]          
Assets held in mutual funds       4,386,000us-gaap_RestrictedInvestments
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
 
Restricted investments       2,856,000us-gaap_RestrictedInvestmentsCurrent
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
 
Trading gains and offsetting compensation expense     95,000us-gaap_UnrealizedGainLossOnSecurities
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
364,000us-gaap_UnrealizedGainLossOnSecurities
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
329,000us-gaap_UnrealizedGainLossOnSecurities
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
Distributions from the deferred compensation plan aggregated     2,893,000us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
864,000us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
357,000us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
Maximum [Member]          
Investments And Employee Deferred Compensation Plan [Line Items]          
Matching contribution on deferred amount 10,000us-gaap_DeferredCompensationArrangementWithIndividualEmployerContribution
/ us-gaap_RangeAxis
= us-gaap_MaximumMember