NATURE OF OPERATIONS AND ACCOUNTING POLICIES - ERA Savings Plan (Details) - USD ($) $ in Millions  | 
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2019  | 
Dec. 31, 2018  | 
Dec. 31, 2017  | 
|
| Organization, Consolidation and Presentation of Financial Statements [Abstract] | |||
| Percent of employer contribution | 3.00% | ||
| Employer matching contribution, percent | 100.00% | ||
| Employer matching contribution, percent of employees' gross pay | 3.00% | ||
| Employer contribution | $ 2.5 | $ 2.3 | $ 2.4 | 
| X | ||||||||||
- Definition Defined Contribution Plan, Percent of Employees' Gross Pay No definition available. 
  | 
| 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 Percentage employer matches of the employee's percentage contribution matched. No definition available. 
  | 
| X | ||||||||||
- References No definition available. 
  |