Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Name:	us-gaap_GoodwillImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Summary of significant accounting policies (Goodwill Impairment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Impairment of goodwill	$ 167	$ 200	$ 5,045
Peru
Goodwill [Line Items]
Impairment of goodwill	$ 167
Mexico
Goodwill [Line Items]
Impairment of goodwill		$ 200	$ 5,045