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Stock Plans - Additional Information (Details)
3 Months Ended 9 Months Ended
Mar. 31, 2018
Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Percentage of target award based on achieving specified performance targets 93.60%  
Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Percentage of target award based on achieving targeted performance conditions 0.00%  
Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Percentage of target award based on achieving targeted performance conditions 200.00%  
Performance Shares    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Fair value assumptions, average closing price used to calculate expected dividend rate, period (years)   1 year
Stock beta, daily price data period (years)   10 years
Performance Shares    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Award vesting period (in years) 3 years