Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation Narrative (Details)

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Stock-Based Compensation Narrative (Details) - 2007 Stock Incentive Plan - shares
3 Months Ended 9 Months Ended
May 10, 2018
Sep. 30, 2018
Mar. 31, 2018
Sep. 30, 2017
Mar. 31, 2017
Sep. 30, 2018
Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Additional shares authorized (in shares) 500,000            
Shares authorized (in shares) 3,230,320            
Performance stock units              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Equity instruments other than options, granted (in shares)   0   0   168,500 166,149
Equity instruments other than options, vested (in shares)         116,168    
Shares issued (in shares)     25,726        
Award vesting rights, percentage     22.10%