Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation (Details)

v3.8.0.1
Stock Based Compensation (Details) - Employee Stock Option [Member] - $ / shares
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Shares - Nonvested, Beginning Balance (in shares) 30,690 28,465
Shares - Granted (in shares) 4,433 4,575
Shares - Vested (in shares) (3,200) (1,625)
Shares - Forfeited (in shares) 0 (725)
Shares - Nonvested, Ending Balance (in shares) 31,923 30,690
Weighted-Average Grant Date Fair Value - Nonvested, Beginning Balance (in dollars per share) $ 28.51 $ 26.67
Weighted-Average Grant Date Fair Value - Granted (in dollars per share) 43.50 39.00
Weighted-Average Grant Date Fair Value - Vested (in dollars per share) 21.00 25.81
Weighted-Average Grant Date Fair Value - Forfeited (in dollars per share)   28.62
Weighted-Average Grant Date Fair Value - Nonvested, Ending Balance (in dollars per share) $ 31.34 $ 28.51