Accounts receivable, net (Details) ¥ in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2017 CNY (¥)	Dec. 31, 2016 CNY (¥)	Dec. 31, 2015 CNY (¥)	Dec. 31, 2017 CNY (¥)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 CNY (¥)
Accounts Receivable Net [Line Items]
Accounts receivable, gross				¥ 161,300		¥ 224,791
Less: allowance for doubtful receivables	¥ (55,220)	¥ (55,220)	¥ (57,342)	(7,356)		(55,220)
Accounts receivable, net				¥ 153,944	$ 23,661	¥ 169,571
Summary of allowance for doubtful accounts
Balance at the beginning of the year	(55,220)	(58,791)	(57,342)
(Additions) reversals charged to general and administrative expenses, net	(3,049)	3,571	(1,449)
Write-off during the year	50,913	0	0
Balance at the end of the year	¥ (7,356)	¥ (55,220)	¥ (58,791)

Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
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- Definition

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of direct write-downs of accounts receivable charged against the allowance.

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Additions To Allowance For Doubtful Accounts.

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