SUBSEQUENT EVENTS (Details) (Needham, MA office lease agreement, USD $) In Millions, unless otherwise specified	0 Months Ended
	Apr. 11, 2013
Subsequent events
Leasable space of the office (in square feet)	40,066
Subsequent event
Subsequent events
Modification fees in connection with the amendment of lease agreement	$ 0.8
Subsequent event | Leasable space from January 1, 2013 to March 31, 2013
Subsequent events
Leasable space of the office (in square feet)	45,955
Subsequent event | Leasable space from April 1, 2013 to June 30, 2013
Subsequent events
Leasable space of the office (in square feet)	44,825
Subsequent event | Leasable space from July 1, 2013 to June 30, 2023
Subsequent events
Leasable space of the office (in square feet)	19,368