Segment Information - Summary of Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Segment revenues:
Revenues		$ 278,234	$ 256,260	$ 540,490	$ 488,621
Segment operating expense		(229,685)	(209,821)	(442,937)	(405,357)
Operating income		48,549	46,439	97,553	83,264
Unallocated share-based compensation expense		(20,482)	(19,239)	(42,336)	(35,749)
Unallocated amortization expense	[1]	(1,503)	(1,684)	(3,005)	(3,472)
Unallocated interest expense		(10,008)	(7,116)	(19,684)	(13,576)
Unallocated other income, net		1,433	(161)	(739)	352
Income before income taxes		39,974	39,162	77,130	70,040
Depreciation expense		5,995	5,510	12,139	11,304
Operating Segments
Segment revenues:
Segment operating expense		(207,700)	(188,898)	(397,596)	(366,136)
Operating income		70,534	67,362	142,894	122,485
Unallocated Corporate Expenses
Segment revenues:
Segment operating expense		(39,506)	(33,493)	(68,760)	(60,254)
Operating income		(39,506)	(33,493)	(68,760)	(60,254)
Depreciation expense		229	238	462	522
Applications
Segment revenues:
Revenues		141,815	146,496	289,474	286,670
Applications | Operating Segments
Segment revenues:
Revenues		141,815	146,496	289,474	286,670
Segment operating expense		(111,643)	(107,292)	(219,241)	(210,018)
Operating income		30,172	39,204	70,233	76,652
Depreciation expense		4,662	3,834	9,459	7,777
Scores
Segment revenues:
Revenues		104,403	87,103	190,086	155,534
Scores | Operating Segments
Segment revenues:
Revenues		104,403	87,103	190,086	155,534
Segment operating expense		(16,167)	(16,413)	(29,649)	(32,301)
Operating income		88,236	70,690	160,437	123,233
Depreciation expense		132	147	257	302
Decision Management Software
Segment revenues:
Revenues		32,016	22,661	60,930	46,417
Decision Management Software | Operating Segments
Segment revenues:
Revenues		32,016	22,661	60,930	46,417
Segment operating expense		(40,384)	(31,700)	(79,946)	(63,563)
Operating income		(8,368)	(9,039)	(19,016)	(17,146)
Depreciation expense		972	1,291	1,961	2,703
Transactional and Maintenance
Segment revenues:
Revenues		211,779	192,791	405,972	363,194
Transactional and Maintenance | Applications | Operating Segments
Segment revenues:
Revenues		97,074	95,515	194,239	186,641
Transactional and Maintenance | Scores | Operating Segments
Segment revenues:
Revenues		102,363	85,451	187,184	153,447
Transactional and Maintenance | Decision Management Software | Operating Segments
Segment revenues:
Revenues		12,342	11,825	24,549	23,106
Technology Service
Segment revenues:
Revenues		50,555	46,731	91,363	89,859
Technology Service | Applications | Operating Segments
Segment revenues:
Revenues		35,981	39,131	67,443	74,505
Technology Service | Scores | Operating Segments
Segment revenues:
Revenues		901	757	1,602	1,054
Technology Service | Decision Management Software | Operating Segments
Segment revenues:
Revenues		13,673	6,843	22,318	14,300
License
Segment revenues:
Revenues		15,900	16,738	43,155	35,568
License | Applications | Operating Segments
Segment revenues:
Revenues		8,760	11,850	27,792	25,524
License | Scores | Operating Segments
Segment revenues:
Revenues		1,139	895	1,300	1,033
License | Decision Management Software | Operating Segments
Segment revenues:
Revenues		$ 6,001	$ 3,993	$ 14,063	$ 9,011

[1] Cost of revenues and selling, general and administrative expenses exclude the amortization of intangible assets. See Note 4.