SUMMARY OF OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES - Additional information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Segment	Jun. 30, 2011	Jun. 30, 2012 Minimum	Jun. 30, 2012 Maximum	Jun. 30, 2012 Two Thousand Employee Stock Purchase Plan	Mar. 31, 2000 Two Thousand Employee Stock Purchase Plan	Jun. 30, 2012 Employee Stock Purchase Plan, 2010	Jun. 30, 2010 Employee Stock Purchase Plan, 2010	Jun. 30, 2012 Incentive Stock Option	Jun. 30, 2012 Incentive Stock Option Nineteen Ninety Eight Plan Maximum	Jun. 30, 2012 Incentive Stock Option Two Thousand Plan	Jun. 30, 2012 Incentive Stock Option Nineteen Ninety Eight and Two Thousand Plan	Jun. 30, 2012 Incentive Stock Option Two Thousand Nine Plan	Jun. 30, 2012 Incentive Stock Option Two Thousand Nine Plan 2009 Plan
Organization Consolidation And Summary Of Significant Accounting Policies [Line Items]
Typical service agreements			12 months
Typical service agreements termination notice period					30 days	90 days
Fees and related labor costs, recognition period (current estimate of term of customer relationship)			48 months
Weighted average fair value of stock options granted	$ 8.29	$ 7.07	$ 7.24	$ 6.97
Shares of common stock available for issuance								450,000	899,000	1,000,000	23,817,744	5,850,000	4,150,000	10,000,000	11,427,000
Increase in number of shares of common stock available for issuance															6,000,000	4,250,000
Stock option term			10 years
Unrecognized compensation cost related to nonvested share-based compensation arrangements	$ 28,198		$ 28,198
Weighted average recognition period of unrecognized compensation cost											2 years 1 month 6 days
Shares of common stock available for issuance, expiration date							Apr. 30, 2010
Total value of stock options exercised			13,739
Total intrinsic value of options exercisable	36,071		36,071
Total intrinsic value of nonvested options	44,206		44,206
Total intrinsic value of all outstanding options	80,277		80,277
Effect of option to purchase share of common stock on diluted net income per share	5,315,243	6,963,746	4,141,393	6,744,246
Weighted average exercise price of options	$ 6.87	$ 4.90	$ 5.60	$ 4.77
Number of operating segments			2
Aggregate amortization expense for intangible assets	77	318	153	635
Estimated amortization expense in 2012	874		874
Estimated amortization expense in 2013	4,448		4,448
Estimated amortization expense in 2014	3,661		3,661
Estimated amortization expense in 2015	2,743		2,743
Estimated amortization expense in 2016	2,743		2,743
Estimated amortization expenses thereafter 2016	$ 156		$ 156