Stock-based Compensation - Shares Available for Future Grants and Reserve for Issuance (Parenthetical) (Details) - shares |
Dec. 31, 2015 |
Dec. 31, 2014 |
|---|---|---|
| Director | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Directors deferred compensation account (in shares) | 142,913 | 135,722 |