Employee Benefit Plan (Details) - USD ($)  | 
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018  | 
Dec. 31, 2017  | 
Dec. 31, 2016  | 
|
| Retirement Benefits [Abstract] | |||
| Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent | 75.00% | ||
| Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay | 6.00% | ||
| Defined Contribution Plan, Contributions | $ 9,000,000 | $ 7,000,000 | $ 6,000,000 | 
| Defined Contribution Plan, Employer Discretionary Contribution Amount | $ 0 | ||
| X | ||||||||||
- References No definition available. 
  | 
| X | ||||||||||
- Definition Amount of cost for defined contribution plan. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
  | 
| X | ||||||||||
- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. No definition available. 
  | 
| X | ||||||||||
- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. No definition available. 
  | 
| X | ||||||||||
- Definition Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan. No definition available. 
  |