Quarterly report pursuant to Section 13 or 15(d)

STOCKHOLDERS' EQUITY - Unvested Restricted Stock Activity (Details)

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STOCKHOLDERS' EQUITY - Unvested Restricted Stock Activity (Details) - Unvested restricted stock
shares in Thousands
6 Months Ended
Jun. 30, 2018
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]  
Unvested Restricted Stock, Beginning Balance (in shares) | shares 2,017
Forfeited (in shares) | shares (17)
Vested (in shares) | shares (593)
Granted (in shares) | shares 428
Unvested Restricted Stock, Ending Balance (in shares) | shares 1,835
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]  
Unvested Restricted Stock, Beginning Balance (in dollars per share) | $ / shares $ 24.50
Forfeited (in dollars per share) | $ / shares 25.42
Vested (in dollars per share) | $ / shares 19.86
Granted (in dollars per share) | $ / shares 48.36
Unvested Restricted Stock, Ending Balance (in dollars per share) | $ / shares $ 31.55