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Share-Based Compensation - Narrative (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Restricted Stock  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Performance units, vesting period (in years) 4 years
Unrecognized compensation cost $ 33.6us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Unrecognized compensation cost, period of recognition (in years) 2 years 2 months 0 days
Restricted Stock Units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Discount from common stock price using a credit spread, percentage 25.90%sd_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodUnitValuationDiscountSpreadOnSharePrice
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Performance Unit and Performance Share Units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Performance units, vesting period (in years) 3 years
Vesting Four Years from Grant Date | Restricted Stock Units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Performance units, vesting period (in years) 4 years
Unrecognized compensation cost 8.1us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= us-gaap_ShareBasedCompensationAwardTrancheOneMember
Unrecognized compensation cost, period of recognition (in years) 3 years 10 months 25 days
Vesting Two Years from Grant Date | Restricted Stock Units  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Performance units, vesting period (in years) 2 years
Unrecognized compensation cost, period of recognition (in years) 1 year 9 months 0 days
Percentage vesting at the end of the first year 40.00%sd_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPercentageYear1
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Percentage vesting at the end of the second year 60.00%sd_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPercentageYear2
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Unrecognized compensation cost related to unvested two-year restricted stock units $ 3.0us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_VestingAxis
= us-gaap_ShareBasedCompensationAwardTrancheTwoMember