Commitments and contingencies - Additional Information (Narrative) (Details)	Dec. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Auction Rate Securities Committed To Purchase related to settlements with regulators	$ 1,300,000
Equity Securities [Member]
Loss Contingencies [Line Items]
Contractual Obligation	40,000,000.0
Private Equity Funds [Member]
Loss Contingencies [Line Items]
Contractual Obligation	1,200,000
Minimum [Member]
Loss Contingencies [Line Items]
Maximum estimated range of aggregate loss for legal proceedings	0
Maximum [Member]
Loss Contingencies [Line Items]
Maximum estimated range of aggregate loss for legal proceedings	$ 5,000,000.0

Auction Rate Securities Committed To Purchase related to settlements with regulators

No definition available.

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- Definition

Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

The difference between the maximum amount of estimated loss and the amount recorded as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 05
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=99385795&loc=d3e12631-108344

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