4.	ACCOUNTS RECEIVABLE, NET

Accounts receivable and allowance for doubtful accounts consist of the following:

 

		December 31,
		2016				2017
		RMB				RMB				US$
Accounts receivable			1,206,436				1,895,145				291,278
Allowance for doubtful accounts			(512	)			(1,408	)			(216	)
Total			1,205,924				1,893,737				291,062

As of December 31, 2016 and 2017, all accounts receivable were due from third party customers.

An analysis of the allowance for doubtful accounts is as follows:

 

		December 31,
		2016				2017
		RMB				RMB				US$
Beginning balance			2,315				512				79
Additions charged to bad debt expense			2,792				1,854				284
Reversal			(489	)			(744	)			(114	)
Write off			(4,106	)			(214	)			(33	)
Ending balance			512				1,408				216

The Group recognized additions to allowance for doubtful accounts amounting to RMB2,179, RMB2,303 and RMB1,110 (US$170) within general and administrative expenses, for the years ended December 31, 2015, 2016 and 2017, respectively.