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Retirement Plan - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Schedule Of Sale Of Subsidiary [Abstract]      
Employers' sponsors contribution retirement plan 90.00%us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent    
Contribution to retirement plan, percentage of employee contribution 100.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent    
Percentage of employee contribution to retirement plan 5.00%us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch    
Employers' sponsors contribution retirement plan amount $ 0.2us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount $ 0.2us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount $ 0.1us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount