STOCK-BASED COMPENSATION (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Stock options
Stock-Based Compensation
Shares available for issuance	2,102,942
Shares
Options Outstanding at beginning of the period (in shares)	5,349,810
Granted (in shares)	1,252,000
Exercised (in shares)	(816,405)
Canceled (in shares)	(14,861)
Options Outstanding at the end of the period (in shares)	5,770,544	5,349,810
Options Vested and Expected to Vest at the end of the period (in shares)	5,712,596
Options Exercisable at the end of the period (in shares)	3,297,190
Shares Available for Grant under the 2008 Plan (in shares)	2,102,942
Weighted Average Exercise Price Per Share
Options Outstanding at beginning of the period (in dollars per share)	$ 5.98
Granted (in dollars per share)	$ 16.44
Exercised (in dollars per share)	$ 6.53
Canceled (in dollars per share)	$ 6.97
Options Outstanding at the end of the period (in dollars per share)	$ 8.17	$ 5.98
Options Vested and Expected to Vest at the end of the period (in dollars per share)	$ 8.12
Options Exercisable at the end of the period (in dollars per share)	$ 6.30
Weighted Average Remaining Contractual Term
Options Outstanding at beginning of the period	7 years	7 years
Options Outstanding at the end of the period	7 years	7 years
Options Vested and Expected to Vest at the end of the period	7 years
Options Exercisable at the end of the period	5 years 7 months 6 days
Additional information
Total intrinsic value of stock options exercised (in dollars)	$ 10.00	$ 0.20	$ 0.03
Weighted average grant-date fair value (in dollars per share)	$ 10.51	$ 3.67	$ 1.83
Fair value of stock options vested (in dollars)	2.4	2.1	2.6
Aggregate intrinsic value of stock options outstanding (in dollars)	92.6
Aggregate intrinsic value of stock options vested and expected to vest (in dollars)	91.9
Total compensation cost not yet recognized (in dollars)	$ 14.4
Weighted average period over which compensation cost is expected to be recognized as expense	2 years 9 months 18 days
Restricted stock
Shares
Outstanding and unvested at the beginning of the period (in shares)	6,000
Granted (in shares)	12,000
Vested (in shares)	(12,000)
Outstanding and unvested at the end of the period (in shares)	6,000
Weighted Average Grant Date Fair Value (per share)
Outstanding and unvested at the beginning of the period (in dollars per share)	$ 4.50
Granted (in dollars per share)	$ 15.20
Vested (in dollars per share)	$ 9.85
Outstanding and unvested at the end of the period (in dollars per share)	$ 15.20
Celldex Research 2005 Plan and CuraGen 2007 Plan
Stock-Based Compensation
Shares available for issuance	0
Shares
Shares Available for Grant under the 2008 Plan (in shares)	0
2004 ESPP Plan
Stock-Based Compensation
Common stock reserved for issuance (in shares)	200,000
Purchase price as a percentage of the lower of the fair market value of the common stock at either the beginning of the offering period or the applicable exercise date	85.00%
Shares issued under the plan	11,823	5,935
Shares available for issuance	164,124
Shares
Shares Available for Grant under the 2008 Plan (in shares)	164,124
2008 Plan
Stock-Based Compensation
Maximum shares of common stock to be issued for grants (in shares)	7,400,000
Terms of options granted to the holders of more than 10% of the voting stock	5 years
Threshold percentage of voting stock	10.00%
Exercise price as a percentage of fair market value for options granted to the holders of more than 10% of the voting stock	110.00%
2008 Plan | Maximum
Stock-Based Compensation
Vesting period	4 years
Terms of options	10 years