XML 116 R86.htm IDEA: XBRL DOCUMENT v3.8.0.1
Stock-Based Compensation (Summary of Stock Option Activity) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stock-Based Compensation [Abstract]      
Options, Outstanding, beginning of period 225,669 276,807 294,720
Options, Granted 34,750 24,000 21,750
Options, Exercised (44,219) (46,235) (25,289)
Options, Forfeited (3,475) (28,904) (14,375)
Options, Outstanding, end of period 212,725 225,669 276,807
Options, Exercisable, end of period 177,975 216,644 270,032
Weighted Average Exercise Price Per Share, Outstanding, beginning of period $ 19.46 $ 17.94 $ 17.83
Weighted Average Exercise Price Per Share, Granted 32.81 22.37 19.03
Weighted Average Exercise Price Per Share, Exercised 23.53 18.23 17.46
Weighted Average Exercise Price Per Share, Forfeited 21.71 18.57 18.01
Weighted Average Exercise Price Per Share, Outstanding, end of period 20.76 19.46 17.94
Weighted Average Exercise Price Per Share, Exercisable, end of period $ 18.41 $ 17.59 $ 17.85
Weighted Average Remaining Contractual Term, Outstanding 6 years 1 month 6 days    
Aggregate Intrinsic Value, Outstanding, beginning of period $ 931,963 $ 362,754  
Aggregate Intrinsic Value, Outstanding, end of period 2,604,097 931,963 $ 362,754
Aggregate Intrinsic Value, Exercisable at end of period $ 2,597,494 $ 931,963 $ 359,854