STOCKHOLDERS' EQUITY (Award Compensation Narrative) (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) Plan Schedule $ / shares shares	Mar. 31, 2017 USD ($) $ / shares		Jul. 31, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program, authorized amount				$ 200,000,000
Stock repurchased during period (in shares) | shares	910,332
Stock repurchased during period, value	$ 37,000,000
Repurchase of common stock	$ 33,309,000	$ 0	[1]
Stock repurchased in cash during period (in shares) | shares	821,968
Treasury stock acquired (in shares) | shares	360,380
Number of equity incentive plans | Plan	3
Stock-based compensation	$ 27,734,000	24,334,000
Capitalized stock-based compensation expense	$ 1,800,000	1,400,000
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of vesting schedules | Schedule	4
Exercisable period	10 years
Intrinsic value of options exercised	$ 8,000,000	$ 4,900,000
Weighted average grant date fair value (in USD per share) | $ / shares	$ 18.78	$ 15.53
Unrecognized compensation costs	$ 26,700,000
Unrecognized compensation costs, period for recognition	2 years 10 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	$ 253,100,000
Unrecognized compensation costs, period for recognition	2 years 8 months
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%
Purchase price, percentage of fair market value	85.00%
Stock-based compensation	$ 600,000	$ 600,000
Minimum | Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Maximum | Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years

[1] As of January 1, 2018, the Company adopted ASC 606 using the full retrospective method. Accordingly, the Company has recast certain amounts in the prior period presented. See Note 1 below for additional discussion.Also as of January 1, 2018, the Company adopted Accounting Standards Update No. 2016-18, "Statement of Cash Flows (Subtopic 230): Restricted Cash," and recast the prior period presented. See Note 1 below for additional discussion.