17 COMMITMENTS AND CONTINGENCIES Operating lease commitments RMB US$ 2016 5,396 833 2017 3,931 607 2018 3,865 597 2019 1,664 258 2020 and thereafter - - 14,856 2,294 Payments under operating leases are expensed on a straight-line basis over the periods of their respective leases. The Group's lease arrangements have no renewal options, rent escalation clauses, restrictions or contingent rents and are all conducted with third parties. For the years ended December 31, 2013, 2014 and 2015, total rental expenses for all operating leases amounted to approximately RMB 4,931 , RMB5,279 and RMB 4,013 (US$ 620 ), respectively. Income taxes As of December 31, 2014 and 2015, the Group has recognized approximately RMB 40,287 and RMB 41,981 (US$ 6,481 ), respectively, as an accrual for unrecognized tax benefits, including related interest and penalties. The final outcome of the tax uncertainty is dependent upon various matters including tax examinations, interpretation of tax laws or expiration of status of limitation. However, due to the uncertainties associated with the status of examinations, including the protocols of finalizing audits by the relevant tax authorities, there is a high degree of uncertainty regarding the future cash outflows associated with these tax uncertainties. As of December 31, 2014, and 2015, the Group classified the accrual of RMB40,287 and RMB41,981 (US$6,481), respectively, as a long-term payable. Variable interest entity structure In the opinion of management, (i) the ownership structure of the Company and its VIEs are in compliance with existing PRC laws and regulations; (ii) the contractual arrangements with the VIEs and their shareholders are valid and binding, and will not result in any violation of PRC laws or regulations currently in effect; and (iii) the Group's business operations are in compliance with existing PRC laws and regulations in all material respects. However, there are substantial uncertainties regarding the interpretation and application of current and future PRC laws and regu