Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Interim financial statements - Narrative (Details) - USD ($)	Jun. 30, 2020	May 07, 2020	May 06, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Investments restricted for statutory reserve funds	$ 504,200,000			$ 483,400,000
Restricted cash and cash equivalent	$ 39,400,000			$ 39,700,000
Amended Credit Agreement \| Line of Credit
Debt Instrument [Line Items]
Line of credit facility		$ 200,000,000.0	$ 150,000,000.0
Line of credit additional		$ 50,000,000.0