STOCK-BASED COMPENSATION - Stock Option Activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Options
Beginning balance (in shares)	5,610,361
Granted (in shares)	2,106,500
Exercised (in shares)	(1,728,186)
Forfeited and expired (in shares)	(1,103,460)
Ending balance (in shares)	4,885,215	5,610,361
Outstanding options less expected forfeitures at December 31, 2012 (in shares)	4,547,982
Exercisable at December 31, 2012 (in shares)	1,872,364
Weighted Average Exercise Price
Beginning balance (dollars per share)	$ 5.94
Granted (dollars per share)	$ 6.79
Exercised (dollars per share)	$ 5.01
Forfeited and expired (dollars per share)	$ 8.90
Ending balance (dollars per share)	$ 5.97	$ 5.94
Outstanding options less expected forfeitures at December 31, 2012 (dollars per share)	$ 5.96
Exercisable at December 31, 2012 (dollars per share)	$ 5.36
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Aggregate intrinsic value, balance	$ 23,462,800	$ 4,747,200
Aggregate intrinsic value, outstanding options less expected forfeitures at December 31, 2012	21,890,700
Aggregate intrinsic value, exercisable at December 31, 2012	$ 10,124,100
Weighted average remaining contractual life, balance	7 years 9 months 18 days	5 years 4 months 24 days
Weighted average remaining contractual life, outstanding options less expected forfeitures at December 31, 2012	7 years 8 months 12 days
Weighted average remaining contractual life, exercisable at December 31, 2012	6 years 1 month 6 days