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Compensation Plans - Summary of Restricted Stock Units Activity (Details) - Restricted Stock Units (RSUs)
12 Months Ended
Dec. 31, 2017
$ / shares
shares
Shares  
Outstanding, beginning of period (in shares) | shares 58,698
Granted (in shares) | shares 16,462
Vested (in shares) | shares (33,206)
Forfeited (in shares) | shares (732)
Outstanding, end of period (in shares) | shares 41,222
Weighted Average Grant Date Fair Value  
Outstanding, beginning of period (usd per share) | $ / shares $ 23.06
Granted (usd per share) | $ / shares 41.68
Vested (usd per share) | $ / shares 18.48
Forfeited (usd per share) | $ / shares 14.48
Outstanding, end of period (usd per share) | $ / shares $ 34.34