Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation (Summary of Restricted Stock Unit Activity) (Details)

v3.10.0.1
Stock-Based Compensation (Summary of Restricted Stock Unit Activity) (Details) - Restricted Stock Units (RSUs) [Member] - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock units outstanding, beginning, number of shares 449,475 466,475 553,289
Granted, number of shares 197,299 270,169 205,734
Vested, number of shares (155,847) (176,654) (235,059)
Forfeited, number of shares (66,926) (110,515) (57,489)
Restricted stock units outstanding, ending, number of shares 424,001 449,475 466,475
Restricted stock units outstanding, beginning, weighted average grate date fair value per share $ 52.07 $ 47.23 $ 38.85
Granted, weighted average grant date fair value per share 73.74 52.45 55.93
Vested, weighted average grant date fair value 50.97 42.32 33.98
Forfeited, weighted average grant date fair value 53.19 48.13 46.35
Restricted stock units outstanding, ending, weighted average grate date fair value per share $ 62.38 $ 52.07 $ 47.23