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Stock Based Compensation - Narrative (Details)
$ / shares in Units, $ in Millions
12 Months Ended
Jul. 03, 2017
shares
May 17, 2016
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Dec. 31, 2015
USD ($)
equity_plan
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of equity plans | equity_plan         2
Weighted Average Grant Date Fair Value          
Weighted average grant date fair value, granted (in dollars per share) | $ / shares     $ 18.75 $ 16.82 $ 15.53
Fair values of vested restricted stock and stock options | $     $ 0.1 $ 0.1 $ 0.2
Restricted stock units          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Restricted stock units issued 5,334 8,919      
2015 Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of shares approved         1,500,000
Shares available for future issuance     1,485,747    
Number of Units          
Number of units, vested     2,229 6,690  
2015 Plan | Restricted stock units          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Unvested restricted stock units outstanding     5,334    
Director | 2015 Plan | Restricted Stock          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Restricted stock units issued     5,334 8,919