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Equity Awards - Restricted Stock Units Narrative (Details) - Restricted Stock Units [Member] - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted shares issued related to director fee deferrals 2,657    
Number of Unvested Restricted Stock Units Granted 33,678    
Unrecognized unvested restricted shares-based compensation expense $ 4.3    
Weighted-average period for recognition of the unrecognized unvested restricted shares-based compensation expense 1 year 10 months    
Total shareholder return metric [Member] | Plan 3 [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Unvested Restricted Stock Units Granted 31,021    
Share-based Compensation Arrangement by Share-based Payment Award, Award percentage attained     126.90%
Total shareholder return metric [Member] | Minimum [Member] | Plan 3 [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award percentage earned based on metric over the performance period 0.00%    
Total shareholder return metric [Member] | Maximum [Member] | Plan 3 [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award percentage earned based on metric over the performance period 200.00%    
Selling, General and Administrative Expenses [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted shares-based compensation expense $ 1.1 $ 1.3