Employee Stock and Benefit Plans (Fair Value Assumptions, Stock Options) (Details) - Stock Options |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Dividend yield | 0.00% | 0.00% | 0.00% |
| Minimum | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Expected term | 4 years 10 months 24 days | 5 years 3 months 7 days | 5 years 4 months 24 days |
| Volatility | 45.00% | 48.00% | 52.00% |
| Risk-free interest rate | 1.30% | 1.50% | 0.70% |
| Maximum | |||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Expected term | 5 years 10 months 7 days | 5 years 10 months 7 days | 6 years 1 month 6 days |
| Volatility | 48.00% | 52.00% | 53.00% |
| Risk-free interest rate | 1.70% | 1.70% | 1.50% |