Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Restricted short-term deposits (Narrative) (Details) ¥ in Millions, $ in Millions	Dec. 31, 2018 USD ($)	Dec. 31, 2017 CNY (¥)	Dec. 31, 2017 USD ($)
Restricted Cash And Investments [Line Items]
Debt Instrument, Collateral Amount \| ¥		¥ 1,000
Restricted Of Short Term Deposit	$ 0
Loans Payable [Member]
Restricted Cash And Investments [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity			$ 160