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Employee Benefit Plans - Savings Plans (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended 2 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Mar. 02, 2015
Defined Contribution Plan Disclosure [Line Items]        
Employer discretionary contribution amount $ 3.0us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount $ 2.8us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount $ 2.3us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount  
United States [Member]        
Defined Contribution Plan Disclosure [Line Items]        
Minimum annual contribution employees could elect to contribute, percent 1.00%core_DefinedContributionPlanMinimumAnnualContributionPerEmployeePercent
/ us-gaap_StatementGeographicalAxis
= country_US
     
Maximum annual contribution employees could elect to contribute, percent 75.00%us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent
/ us-gaap_StatementGeographicalAxis
= country_US
     
Percentage of employees' base salary for which Company contributes a matching contribution 3.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
/ us-gaap_StatementGeographicalAxis
= country_US
     
United States [Member] | 2% of base salary [Member]        
Defined Contribution Plan Disclosure [Line Items]        
Employers matching contribution, percent 100.00%core_DefinedContributionPlanEmployersMatchingContributionPercentOfMatch
/ core_EmployeeContributionsPlansAxis
= core_TwoPercentOfBaseSalaryMember
/ us-gaap_StatementGeographicalAxis
= country_US
     
Percentage of employees' base salary for which Company contributes a matching contribution 2.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
/ core_EmployeeContributionsPlansAxis
= core_TwoPercentOfBaseSalaryMember
/ us-gaap_StatementGeographicalAxis
= country_US
     
United States [Member] | 2% to 6% of base salary [Member]        
Defined Contribution Plan Disclosure [Line Items]        
Employers matching contribution, percent 25.00%core_DefinedContributionPlanEmployersMatchingContributionPercentOfMatch
/ core_EmployeeContributionsPlansAxis
= core_TwoToSixPercentOfBaseSalaryMember
/ us-gaap_StatementGeographicalAxis
= country_US
     
United States [Member] | 2% to 6% of base salary [Member] | Minimum [Member]        
Defined Contribution Plan Disclosure [Line Items]        
Percentage of employees' base salary for which Company contributes a matching contribution 2.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
/ core_EmployeeContributionsPlansAxis
= core_TwoToSixPercentOfBaseSalaryMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_StatementGeographicalAxis
= country_US
     
United States [Member] | 2% to 6% of base salary [Member] | Maximum [Member]        
Defined Contribution Plan Disclosure [Line Items]        
Percentage of employees' base salary for which Company contributes a matching contribution 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
/ core_EmployeeContributionsPlansAxis
= core_TwoToSixPercentOfBaseSalaryMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementGeographicalAxis
= country_US
     
Canada [Member]        
Defined Contribution Plan Disclosure [Line Items]        
Percentage of employees' base salary for which Company contributes a matching contribution 3.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
/ us-gaap_StatementGeographicalAxis
= country_CA
     
Canada [Member] | 3% of base salary [Member]        
Defined Contribution Plan Disclosure [Line Items]        
Employers matching contribution, percent 50.00%core_DefinedContributionPlanEmployersMatchingContributionPercentOfMatch
/ core_EmployeeContributionsPlansAxis
= core_ThreePercentOfBaseSalaryMember
/ us-gaap_StatementGeographicalAxis
= country_CA
     
Percentage of employees' base salary for which Company contributes a matching contribution 6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
/ core_EmployeeContributionsPlansAxis
= core_ThreePercentOfBaseSalaryMember
/ us-gaap_StatementGeographicalAxis
= country_CA
     
Subsequent Event [Member] | United States [Member]        
Defined Contribution Plan Disclosure [Line Items]        
Employers matching contribution, percent       50.00%core_DefinedContributionPlanEmployersMatchingContributionPercentOfMatch
/ us-gaap_StatementGeographicalAxis
= country_US
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Percentage of employees' base salary for which Company contributes a matching contribution       6.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
/ us-gaap_StatementGeographicalAxis
= country_US
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember