UNAUDITED SUPPLEMENTARY QUARTERLY INFORMATION (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
UNAUDITED SUPPLEMENTARY QUARTERLY INFORMATION
Net (loss) income	$ (20,989)	$ (13,290)	$ (5,380)	$ (5,211)	$ 2,169	$ (8,072)	$ (1,712)	$ (3,018)	$ (4,491)	$ 4,208	$ 8,353	$ 12,985	$ (44,870)	$ (10,634)	$ 21,055
Net (loss) income per share:
Basic and Diluted (in dollars per share)	$ (0.06)	$ (0.04)	$ (0.02)	$ (0.02)	$ 0.01	$ (0.03)	$ (0.01)	$ (0.01)	$ (0.01)	$ 0.01	$ 0.03	$ 0.04	$ (0.13)	$ (0.03)	$ 0.07
Weighted average common shares outstanding (thousands) (note 12):
Basic (in shares)									299,518,000	298,510,000	298,237,000	298,242,000	337,297,000	313,887,000	298,772,000
Diluted (in shares)									301,102,000	301,045,000	299,791,000	298,554,000	337,297,000	313,887,000	300,474,000
Basic and diluted (in dollars per share)	337,936	337,100	337,087	337,062	313,002,000	314,077,000	308,523,000	299,575,000