Stock Plans and Stock Based Compensation - Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands |
12 Months Ended |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Awards granted (in shares) |
59,333
|
73,716
|
109,750
|
| Stock-based compensation expense |
$ 2,956
|
$ 2,270
|
$ 1,903
|
| 2009 Equity Plan |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Authorized number of awards (in shares) |
1,602,000
|
|
|
| Employee Stock Option |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Options granted during period (in shares) |
0
|
|
|
| Employee Stock Option | 2009 Equity Plan |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Award term (no more than) |
10 years
|
|
|
| Restricted Stock Units (RSUs) |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Awards granted (in shares) |
59,333
|
53,770
|
61,235
|
| Stock-based compensation expense |
$ 2,600
|
$ 1,800
|
$ 1,400
|
| Period for recognition - unrecognized compensation cost (in shares) |
4 years 2 months
|
|
|
| Average grant date fair value (in dollars per share) |
$ 79.51
|
$ 76.93
|
$ 56.29
|
| Unrecognized compensation cost - RSUs |
$ 12,700
|
|
|
| Stock Appreciation Rights (SARs) |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Awards granted (in shares) |
|
19,946
|
48,515
|
| Stock options and SARs granted (in shares) |
0
|
|
|
| Stock Appreciation Rights (SARs) | 2009 Equity Plan |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Award term (no more than) |
10 years
|
|
|
| Stock Options |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Stock-based compensation expense |
$ 367
|
$ 476
|
$ 509
|
| Unrecognized compensation cost - options |
$ 1,000
|
|
|
| Period for recognition - unrecognized compensation cost (in shares) |
3 years 8 months
|
|
|
| Minimum | Employee Stock Option | 2009 Equity Plan |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Award vesting period (in years) |
1 year
|
|
|
| Minimum | Restricted Stock | 2009 Equity Plan |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Award vesting period (in years) |
5 years
|
|
|
| Minimum | Stock Appreciation Rights (SARs) | 2009 Equity Plan |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Award vesting period (in years) |
1 year
|
|
|
| Maximum | Employee Stock Option | 2009 Equity Plan |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Award vesting period (in years) |
7 years
|
|
|
| Maximum | Restricted Stock | 2009 Equity Plan |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Award vesting period (in years) |
7 years
|
|
|
| Maximum | Stock Appreciation Rights (SARs) | 2009 Equity Plan |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Award vesting period (in years) |
7 years
|
|
|