SHAREHOLDERS' EQUITY - Deferred Compensation Arrangement (Details) - USD ($) $ in Thousands	1 Months Ended			12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Compensation Arrangement with Employees and Non-Employees, Share-Based Payments [Line Items]
Fair value of shares withheld for tax withholding obligations				$ 5,337	$ 2,844
Employees and Non Employee Members of Scientific Advisory Board [Member]
Deferred Compensation Arrangement with Employees and Non-Employees, Share-Based Payments [Line Items]
Shares issued (in shares)	35,205	31,301	22,586
Employees [Member]
Deferred Compensation Arrangement with Employees and Non-Employees, Share-Based Payments [Line Items]
Fair value of shares issued					$ 967	$ 749	$ 435
Shares withheld for tax withholding obligations (in shares)				9,565	8,071	4,672
Fair value of shares withheld for tax withholding obligations				$ 346	$ 271	$ 154
Non Employee Members of Scientific Advisory Board [Member]
Deferred Compensation Arrangement with Employees and Non-Employees, Share-Based Payments [Line Items]
Fair value of shares issued					$ 300	$ 323	$ 300