Employee Stock Purchase Plan Stock Options and Warrants - Fair Value Calculation Assumptions (Details) |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Risk-free interest rate, minimum | 1.15% | 1.53% | 1.53% |
Risk-free interest rate, maximum | 1.40% | 1.66% | 1.97% |
Expected option life | 5 years | ||
Expected dividend yield | 0.00% | 0.00% | 0.00% |
Expected price volatility, minimum | 34.28% | 33.72% | 34.52% |
Expected price volatility, maximum | 37.06% | 35.11% | 36.90% |
Minimum | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Expected option life | 5 years | 5 years | |
Maximum | |||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Expected option life | 5 years 6 months |