STOCKHOLDERS' EQUITY (Schedule of Stock by Class) (Details) - $ / shares	Sep. 30, 2017	Dec. 31, 2016	Sep. 23, 2016	Sep. 22, 2016
Stockholders' equity:
Common stock, par value (in USD per share)	$ 0.000001	$ 0.000001
Common stock, shares authorized (in shares)	200,000,000	200,000,000	200,000,000	500,000,000
Common stock, shares issued (in shares)	82,741,466	79,429,833
Common stock, shares outstanding (in shares)	82,741,466	79,429,833
Undesignated preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Undesignated preferred stock, shares issued (in shares)	0	0
Undesignated preferred stock, shares outstanding (in shares)	0	0