THE COMPANY AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Additional Information (Detail) $ in Thousands, shares in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($) category channel	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) category revenue_source channel shares	Sep. 30, 2016 USD ($) shares	Dec. 31, 2016 USD ($)
Organization and Summary of Significant Accounting Policies Disclosure [Line Items]
Number of business channels | channel	2		2
Number of revenue and cost categories | category	2		2
Increased in cash provided by operating activities			$ 48,596	$ 59,716
Increased in cash used in financing activities			(17,364)	(991)
Reduction in provision for income taxes due to excess tax benefits	$ 337	$ 285	$ 1,420	$ 1,362
Unvested service-based restricted stock awards included in the calculation of earnings per share (in shares) | shares			0.6	0.6
Minimum lease commitments under non-cancellable operating leases					$ 17,900
Number of primary revenue sources | revenue_source			3
Deposits Assets
Organization and Summary of Significant Accounting Policies Disclosure [Line Items]
Cash subject to FDIC insurance	8,400		$ 8,400
Cash not subject to FDIC insurance	$ 143,900		143,900
Accounting Standards Update 2016-09
Organization and Summary of Significant Accounting Policies Disclosure [Line Items]
Increased in cash provided by operating activities				$ 2,500
Increased in cash used in financing activities				$ 2,500
Reduction in provision for income taxes due to excess tax benefits			$ 500
Accounting Standards Update 2016-09 | Retained Earnings
Organization and Summary of Significant Accounting Policies Disclosure [Line Items]
Adoption of ASU 2016-09					(400)
Accounting Standards Update 2016-09 | Additional Paid-in Capital
Organization and Summary of Significant Accounting Policies Disclosure [Line Items]
Adoption of ASU 2016-09					$ 400
Transaction-based | Consolidated Revenues | Revenue source
Organization and Summary of Significant Accounting Policies Disclosure [Line Items]
Concentration risk percentage					94.00%
Portal Software Development and Services | Consolidated Revenues | Revenue source
Organization and Summary of Significant Accounting Policies Disclosure [Line Items]
Concentration risk percentage					4.00%
Portal Management and Other Fixed Fee Services | Consolidated Revenues | Revenue source
Organization and Summary of Significant Accounting Policies Disclosure [Line Items]
Concentration risk percentage					2.00%