Summary of Significant Accounting Policies - Revenue Recognition, Cash and Cash Equivalents, and Securities Borrowed and Loaned (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) item
Revenue recognition
Additional fee on unspecified future software upgrades \| $	$ 0.0
Number of revenue recognition criteria \| item	4
Cash and Cash Equivalents
Maximum original maturity period of cash equivalents	3 months
Minimum
Revenue recognition
Term of agreement	1 year
Maximum
Revenue recognition
Term of agreement	3 years

Revenue from providing technology services. The services may include training, installation, engineering or consulting. Consulting services often include implementation support, software design or development, or the customization or modification of the licensed software.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(d))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 605
-Section 25
-Paragraph 76
-URI http://asc.fasb.org/extlink&oid=68047459&loc=d3e132428-111767

Name:	us-gaap_TechnologyServicesRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration