Segment Information - Revenues And Percentage Of Revenues By Reportable Market Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Revenues	$ 235,824	$ 238,778	$ 206,678	$ 200,076	$ 232,756	$ 209,366	$ 207,109	$ 189,550	$ 881,356	$ 838,781	$ 788,985
Product Concentration Risk | Sales Revenue
Segment Reporting Information [Line Items]
Concentration of risk, percentage									100.00%	100.00%	100.00%
Applications
Segment Reporting Information [Line Items]
Revenues									$ 532,642	$ 526,274	$ 504,256
Applications | Product Concentration Risk | Sales Revenue
Segment Reporting Information [Line Items]
Concentration of risk, percentage									61.00%	63.00%	64.00%
Scores
Segment Reporting Information [Line Items]
Revenues									$ 241,059	$ 207,007	$ 186,469
Scores | Product Concentration Risk | Sales Revenue
Segment Reporting Information [Line Items]
Concentration of risk, percentage									27.00%	25.00%	24.00%
Decision Management Software
Segment Reporting Information [Line Items]
Revenues									$ 107,655	$ 105,500	$ 98,260
Decision Management Software | Product Concentration Risk | Sales Revenue
Segment Reporting Information [Line Items]
Concentration of risk, percentage									12.00%	12.00%	12.00%