SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, STOCK BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Stock-Based Compensation Expense [Abstract]
Net cash proceeds from the exercise of stock options and Employee Stock Purchase Plan	$ 646	$ 1,610	$ 5,350	$ 5,157
Excess tax benefits realized from stock option exercised and restricted stock awards vested	418	1,348	7,970	28,167
Compensation expense	$ 9,312	$ 6,647	$ 25,169	$ 20,906
Exercise of stock options (in shares)	0	20,366	41,068	66,201
Cost of Revenues [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	$ 1,533	$ 1,067	$ 4,242	$ 3,331
Selling and Marketing [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,411	954	3,595	2,729
Software Development [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,602	1,179	4,318	3,867
General and Administrative [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	$ 4,766	$ 3,447	$ 13,014	$ 10,979