Borrowings - Security and Settlement (Details) $ in Millions	Dec. 31, 2018 USD ($)
Borrowings
Overdraft facilities outstanding	$ 78.0
Weighted average interest rate on outstanding short-term bank loans to support clearance and settlement activities (as a percent)	1.92%

Weighted average interest rate of short-term debt outstanding calculated at point in time.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant