Stock Plans and Stock Based Compensation - Net Cash Proceeds, Tax Benefits and Intrinsic Value Related to Stock Options, SARs, and Restricted Stock(Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Disclosure of Compensation Related Costs, Share-based Payments [Abstract] | |||
| Net proceeds from stock option exercises | $ (641) | $ (806) | $ 1,382 |
| Tax benefits related to stock option and SAR exercises and vesting of restricted shares | 1,634 | 1,433 | 358 |
| Intrinsic value of stock option exercises | $ 3,139 | $ 3,718 | $ 3,014 |