Organization - Schedule of Assets, Liabilities, and Cash Flows of VIEs (Detail)
¥ in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2017
CNY (¥)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
CNY (¥)
Dec. 31, 2015
CNY (¥)
Dec. 31, 2017
USD ($)
Variable Interest Entity [Line Items]          
Current assets ¥ 10,258,586   ¥ 7,432,532   $ 1,576,718
Non-current assets 2,036,389   1,959,494   312,987
Total assets 12,294,975   9,392,026   1,889,705
Accrued expenses and other payables 1,658,934   1,151,547   254,973
Advance from customers 70,454   75,882   10,829
Deferred revenue 1,409,485   1,012,143   216,634
Income tax payable 144,379   256,775   22,191
Amounts due to related parties 10,285   16,630   1,581
Total current liabilities 3,889,316   2,544,040   597,778
Other liabilities 32,122   34,977   4,937
Deferred tax liabilities 438,251   461,796   67,358
Total non-current liabilities 470,373   496,773   72,295
Total liabilities 4,359,689   3,040,813   670,073
Net revenues 6,210,181 $ 954,487 5,961,621 ¥ 3,463,975  
Net (loss)/income 2,001,619 307,642 1,227,914 990,649  
Net cash (used in)/generated from operating activities 2,473,018 380,096 1,625,896 1,461,841  
Net cash used in investing activities (4,913,827) (755,241) (514,906) (407,657)  
Net cash generated from financing activities 61,070 9,386 27,920 30,200  
VIEs [Member]          
Variable Interest Entity [Line Items]          
Current assets 1,326,075   1,059,117   203,814
Non-current assets 1,645,183   1,643,467   252,860
Total assets 2,971,258   2,702,584   456,674
Accrued expenses and other payables 162,423   191,942   24,964
Advance from customers 45,747   15,452   7,031
Deferred revenue 47,507   40,115   7,302
Income tax payable 0   42,746   0
Amounts due to related parties 4,309   1,430   662
Inter-company payables 1,031,877   761,583   158,597
Total current liabilities 1,291,863   1,053,268   198,556
Other liabilities 20,010   21,131   3,075
Deferred tax liabilities 12,708   7,400   1,953
Total non-current liabilities 32,718   28,531   5,028
Total liabilities 1,324,581   1,081,799   203,584
Net assets 1,646,677   1,620,785   $ 253,090
Net revenues 274,774 42,232 328,618 271,198  
Net (loss)/income 20,380 3,132 (71,931) (68,272)  
Net cash (used in)/generated from operating activities 851,872 130,930 20,337 (23,630)  
Net cash used in investing activities (802,710) (123,374) (33,204) (73,318)  
Net cash generated from financing activities ¥ 0 $ 0 ¥ 0 ¥ 0