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STOCK-BASED COMPENSATION - ESPP (Details) - Employee Stock Purchase Plan - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Jul. 31, 2014
Stock-Based Compensation        
Discount on purchase of common stock (as a percent) 5.00%      
Maximum percentage of payroll deductions on eligible compensation 10.00%      
Maximum stock purchases by employees, value $ 25,000      
Maximum stock purchases by employees (in shares) 1,000      
Shares purchased by employees under the ESPP (in shares) 1,200,000 1,300,000 1,300,000  
Common stock reserved and approved for issuance under the plan (in shares)       25,000,000
Shares available for purchase (in shares) 21,800,000 23,100,000 24,400,000