STOCK-BASED COMPENSATION (Details 3) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Stock options
Weighted-average assumptions
Risk-free interest rate, minimum (as a percent)	0.76%	0.74%	0.76%	0.74%
Risk-free interest rate, maximum (as a percent)	1.30%	1.10%	1.30%	1.17%
Weighted-average estimated fair value of stock options (in dollars per share)	$ 17.64	$ 11.11	$ 15.43	$ 10.37
Stockholders' equity:
Options exercised (in shares)			1,158,057
Exercised, Weighted-Average Exercise Price of Outstanding Options (in dollars per share)			$ 14.95
Total cash proceed			$ 17,315,980
Stock options \| Minimum
Weighted-average assumptions
Expected term	5 years	5 years	5 years	5 years
Volatility (as a percent)	59.00%	55.00%	58.00%	55.00%
Stock options \| Maximum
Weighted-average assumptions
Expected term	6 years	6 years	6 years	6 years
Volatility (as a percent)	60.00%	60.00%	60.00%	60.00%
Employee stock purchase plan issuances
Weighted-average assumptions
Risk-free interest rate, minimum (as a percent)	0.09%	0.15%	0.09%	0.15%
Risk-free interest rate, maximum (as a percent)	0.26%	0.29%	0.26%	0.29%
Weighted-average estimated fair value of stock options (in dollars per share)	$ 16.44	$ 9.00	$ 16.44	$ 9.00
Employee stock purchase plan issuances \| Minimum
Weighted-average assumptions
Expected term	6 months	6 months	6 months	6 months
Volatility (as a percent)	56.00%	55.00%	56.00%	55.00%
Employee stock purchase plan issuances \| Maximum
Weighted-average assumptions
Expected term	2 years	2 years	2 years	2 years
Volatility (as a percent)	61.00%	64.00%	61.00%	64.00%

The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Number of share options (or share units) exercised during the current period.

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