STOCKHOLDERS' EQUITY (Award Compensation Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) Plan Schedule $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Jul. 31, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program, authorized amount					$ 200,000,000
Shares repurchased and retired (in shares) | shares	185,592
Value of shares repurchased and retired	$ 7,700,000
Number of equity incentive plans | Plan			3
Stock-based compensation	25,309,000	$ 22,560,000	$ 75,007,000	$ 62,396,000
Capitalized stock-based compensation expense	1,500,000	1,300,000	$ 4,600,000	3,300,000
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Number of vesting schedules | Schedule			4
Exercisable period			10 years
Intrinsic value of options exercised	$ 9,800,000	$ 10,200,000	$ 20,200,000	$ 14,900,000
Weighted average grant date fair value (in USD per share) | $ / shares	$ 13.31	$ 13.16	$ 15.35	$ 9.60
Unrecognized compensation costs	$ 21,300,000		$ 21,300,000
Unrecognized compensation costs, period for recognition			2 years 6 months
Employee Stock Option | End of year one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			25.00%
Employee Stock Option | First year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			10.00%
Employee Stock Option | Second year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			20.00%
Employee Stock Option | Third year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			30.00%
Employee Stock Option | Fourth year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			40.00%
Employee Stock Option | Monthly Basis First Year Member
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			35.00%
Employee Stock Option | Monthly Basis Second Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			40.00%
Employee Stock Option | Monthly Basis Third Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			25.00%
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
Number of vesting schedules | Schedule			3
Unrecognized compensation costs	$ 234,700,000		$ 234,700,000
Unrecognized compensation costs, period for recognition			2 years 9 months 18 days
RSUs | End of year one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			25.00%
RSUs | First year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			10.00%
RSUs | Second year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			20.00%
RSUs | Third year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			30.00%
RSUs | Fourth year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate			40.00%
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Subscription rate of eligible compensation	15.00%		15.00%
Purchase price, percentage of fair market value			85.00%
Number of shares purchased (in shares) | shares	0	0	228,299	200,953
Weighted-average purchase price (in USD per share) | $ / shares	$ 23.73	$ 22.26	$ 23.73	$ 22.26
Stock-based compensation	$ 500,000	$ 400,000	$ 1,500,000	$ 1,100,000