Retained earnings - Appropriated (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019
Retained earnings
Balance at beginning of the period	$ 11,265	$ 11,265	$ 11,104	$ 11,104	$ 11,104
Balance at end of the period	$ 11,265	$ 11,265	$ 11,265	$ 11,104	$ 11,104

A segregation of retained earnings which is unavailable for dividend distribution. Includes also retained earnings appropriated for loss contingencies.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Name:	us-gaap_RetainedEarningsAppropriated
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant