STOCKHOLDERS' EQUITY (Details) - USD ($)						1 Months Ended				12 Months Ended
	Dec. 22, 2019	Mar. 01, 2019	Jan. 01, 2017	Jul. 28, 2014	Jul. 18, 2014	Jun. 30, 2018	May 31, 2017	Mar. 31, 2017	Dec. 31, 2014	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2016
Number of rights for each outstanding share of common stock				1
Number of shares each right entitles registered holder to purchase				0.0001
Number of days after which right become exercisable				10 days
Preferred stock, purchase price				$ 100.00
Preferred stock, shares authorized										10,000,000	10,000,000
Preferred stock, par value (in dollars per share)										$ 0.001	$ 0.001
Common stock, par value (in dollars per share)										$ 0.001	$ 0.001
Stock Issued During Period, Shares, New Issues	5,434,783	4,100,000						769,230
Period of underwriter overallotment option								30 days
Payments of underwriting discounts and offering expenses		$ 200,000						$ 3,600,000
Incremental stock Based compensation expense			$ 0
Options outstanding										2,605,730	1,916,900
Share Price	$ 9.20	$ 5.87						$ 9.75
Net proceeds		$ 27,500,000
Proceeds from offering	$ 50,000,000.0							$ 54,000,000
Common stock that remains available for sale										$ 9,500,000
Common Stock, Shares Authorized										150,000,000	150,000,000
Percent of commission rate							3.00%		3.00%
Number of years before Rights will expire					10 years
Expenses on stock options								$ 5,128,206		$ 7,800,000	$ 12,900,000	$ 15,900,000
Total unrecognized compensation expense related to unvested time-based restricted stock										$ 15,300,000
Weighted-average period of recognition for total unrecognized compensation expense related to unvested time-based restricted stock										1 year
Recognized stock based compensation expense										$ 11,335,000	$ 12,886,000	$ 15,945,000
Treasury Stock, Shares										41,309	41,309
Treasury Stock, Value										$ 234,000	$ 234,000
Class of Warrant or Right, Outstanding										0	0	0
Over-Allotment Option [Member]
Stock Issued During Period, Shares, New Issues		615,000
Period of underwriter overallotment option		30 days
2015 ATM [Member]
Stock Issued During Period, Shares, New Issues												3,104,253
Gross proceeds												$ 31,600,000
Share Price												$ 10.18
Proceeds from offering												$ 31,000,000.0
2017 ATM [Member]
Stock Issued During Period, Shares, New Issues										13,620,165	9,025,222
Gross proceeds										$ 99,300,000	$ 115,800,000
Share Price										$ 7.29	$ 12.83
Net proceeds										$ 97,500,000	$ 113,700,000
Series A Preferred Stock [Member]
Preferred stock, par value (in dollars per share)										$ 0.001	$ 0.001
Minimum [Member]
Market capitalization thresholds			375,000,000
Maximum [Member]
Market capitalization thresholds			$ 750,000,000
Proceeds from offering							$ 300,000,000		$ 250,000,000				$ 175,000,000.0
Share-based Payment Arrangement, Nonemployee [Member]
Restricted stock outstanding										2,021,250
Employee Stock Option [Member]
Expenses on stock options										$ 3,500,000	$ 0	$ 0
Total unrecognized compensation expense related to unvested time-based restricted stock										$ 2,600,000
Weighted-average period of recognition for total unrecognized compensation expense related to unvested time-based restricted stock										1 year 6 months
Recognized stock based compensation expense										$ 300,000
Unvested restricted stock [Member]
Number of shares granted										1,851,520	1,562,211	1,836,511
Restricted stock outstanding										7,091,789	6,095,692	6,321,643		8,642,055
Milestone Based Restricted Stock [Member]
Restricted stock outstanding										1,103,011
Amended and Restated 2012 Incentive Plan [Member]
Number of shares added to the plan						6,000,000
Number of additional shares that may be issued											779,346
Amended and Restated 2012 Incentive Plan [Member] | Caribe BioAdvisors, L L C [Member] | Unvested restricted stock [Member]
Number of shares granted			2,960,000
Amended and Restated 2012 Incentive Plan [Member] | Michael S. Weiss Executive Chairman And Chief Executive Officer And President [Member] | Unvested restricted stock [Member]
Number Of previously granted shares agreed to be forfeited			3,381,866
Vesting period of previously granted shares			3 years
Number of shares granted			418,371