Goodwill and Intangible Assets - Summary of Changes to Goodwill (Detail) $ in Thousands	6 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill [Roll Forward]
Balance at September 30, 2017	$ 804,414
Foreign currency translation adjustment	8,693
Balance at March 31, 2018	813,107
Applications
Goodwill [Roll Forward]
Balance at September 30, 2017	588,288
Foreign currency translation adjustment	7,959
Balance at March 31, 2018	596,247
Scores
Goodwill [Roll Forward]
Balance at September 30, 2017	146,648
Foreign currency translation adjustment	0
Balance at March 31, 2018	146,648
Decision Management Software
Goodwill [Roll Forward]
Balance at September 30, 2017	69,478
Foreign currency translation adjustment	734
Balance at March 31, 2018	$ 70,212