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Stock-Based Compensation - Assumptions Used Estimate Fair Value of Employee Stock Purchase Plans (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
6 Months Ended 12 Months Ended 6 Months Ended
Sep. 30, 2014
Mar. 31, 2014
Sep. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Shares purchased for offering period 13,619us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans 13,734us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans 19,490us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans 18,594us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans        
Fair value per share $ 0.83smsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePerShare $ 0.30smsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePerShare $ 0.44smsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePerShare $ 0.65smsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePerShare        
Assumptions                
Risk-free interest rate (average) 0.80%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate 0.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate 0.11%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate 0.14%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate 1.20%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate 0.60%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate 0.50%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate  
Expected dividend yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate  
Weighted average expected life (years) 6 months 6 months 6 months 6 months 4 years 4 years 4 years  
Volatility (average) 74.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate 44.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate 45.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate 74.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate 82.90%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate 68.10%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate 80.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate  
Scenario, Forecast [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Fair value per share               $ 0.43smsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsFairValuePerShare
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
Assumptions                
Risk-free interest rate (average)               0.40%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
Expected dividend yield               0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember
Weighted average expected life (years)               6 months
Volatility (average)               109.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate
/ us-gaap_StatementScenarioAxis
= us-gaap_ScenarioForecastMember