Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans (Details)

v2.4.1.9
Employee Benefit Plans (Details) (USD $)
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Employee Benefit Plans      
Maximum employee contribution as percentage of their eligible compensation 90.00%cpst_DefinedContributionPlanMaximumEmployeeContributionAsPercentageOfTheirEligibleCompensation    
Employer's matching contribution on the dollar up to 4% of the employee's contributions (as a percent) 50.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent    
Maximum percentage of employee's contributions for employer's matching contribution of 50 cents for every dollar contributed by employees 4.00%cpst_DefinedContributionPlanMaximumPercentageOfEmployeesContributionForEmployersMatchingContributionOf50CentsForEveryDollarContributionByEmployees    
Employer's contributions made since the inception of the plan $ 0us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount    
Employer's match vesting percentage 25.00%us-gaap_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPercentage    
Employer's match vesting period starting from employee's hire date 4 years    
Expense recorded $ 300,000us-gaap_DefinedContributionPlanCostRecognized $ 300,000us-gaap_DefinedContributionPlanCostRecognized $ 200,000us-gaap_DefinedContributionPlanCostRecognized