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
3 Months Ended
Mar. 31, 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 (5)
Vested (in shares) | shares (586)
Granted (in shares) | shares 384
Unvested Restricted Stock, Ending Balance (in shares) | shares 1,810
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]  
Unvested Restricted Stock (in dollars per share) | $ / shares $ 24.50
Forfeited (in dollars per share) | $ / shares 18.68
Vested (in dollars per share) | $ / shares 19.69
Granted (in dollars per share) | $ / shares 47.88
Unvested Restricted Stock (in dollars per share) | $ / shares $ 31.00