Revenue from Contracts with Customers Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 278,234	$ 256,260	$ 540,490	$ 488,621
Applications
Disaggregation of Revenue [Line Items]
Revenues	141,815	146,496	289,474	286,670
Scores
Disaggregation of Revenue [Line Items]
Revenues	104,403	87,103	190,086	155,534
Decision Management Software
Disaggregation of Revenue [Line Items]
Revenues	32,016	22,661	60,930	46,417
North America
Disaggregation of Revenue [Line Items]
Revenues	204,317	183,969	381,163	347,387
North America | Applications
Disaggregation of Revenue [Line Items]
Revenues	87,226	86,363	168,175	170,102
North America | Scores
Disaggregation of Revenue [Line Items]
Revenues	100,491	84,829	182,564	151,442
North America | Decision Management Software
Disaggregation of Revenue [Line Items]
Revenues	16,600	12,777	30,424	25,843
Latin America
Disaggregation of Revenue [Line Items]
Revenues	11,365	8,037	35,357	15,723
Latin America | Applications
Disaggregation of Revenue [Line Items]
Revenues	6,670	6,534	24,923	12,167
Latin America | Scores
Disaggregation of Revenue [Line Items]
Revenues	1,368	376	1,882	1,085
Latin America | Decision Management Software
Disaggregation of Revenue [Line Items]
Revenues	3,327	1,127	8,552	2,471
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	41,883	43,512	82,103	86,308
Europe, Middle East and Africa | Applications
Disaggregation of Revenue [Line Items]
Revenues	33,238	37,096	65,800	73,312
Europe, Middle East and Africa | Scores
Disaggregation of Revenue [Line Items]
Revenues	1,472	897	3,006	1,755
Europe, Middle East and Africa | Decision Management Software
Disaggregation of Revenue [Line Items]
Revenues	7,173	5,519	13,297	11,241
Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	20,669	20,742	41,867	39,203
Asia Pacific | Applications
Disaggregation of Revenue [Line Items]
Revenues	14,681	16,503	30,576	31,089
Asia Pacific | Scores
Disaggregation of Revenue [Line Items]
Revenues	1,072	1,001	2,634	1,252
Asia Pacific | Decision Management Software
Disaggregation of Revenue [Line Items]
Revenues	4,916	3,238	8,657	6,862
On-Premises [Member]
Disaggregation of Revenue [Line Items]
Revenues	107,036	106,055	220,240	213,751
On-Premises [Member] | Applications
Disaggregation of Revenue [Line Items]
Revenues	81,311	86,332	170,906	172,653
On-Premises [Member] | Scores
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
On-Premises [Member] | Decision Management Software
Disaggregation of Revenue [Line Items]
Revenues	25,725	19,723	49,334	41,098
SaaS Products [Member]
Disaggregation of Revenue [Line Items]
Revenues	66,795	63,102	130,164	119,336
SaaS Products [Member] | Applications
Disaggregation of Revenue [Line Items]
Revenues	60,504	60,164	118,568	114,017
SaaS Products [Member] | Scores
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
SaaS Products [Member] | Decision Management Software
Disaggregation of Revenue [Line Items]
Revenues	6,291	2,938	11,596	5,319
Scores Products [Member]
Disaggregation of Revenue [Line Items]
Revenues	104,403	87,103	190,086	155,534
Scores Products [Member] | Applications
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Scores Products [Member] | Scores
Disaggregation of Revenue [Line Items]
Revenues	104,403	87,103	190,086	155,534
Scores Products [Member] | Decision Management Software
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 0	$ 0	$ 0