Condensed Financial Information of the Parent Company - Condensed Statements of Comprehensive Income (Detail) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014 USD ($)	Dec. 31, 2014 CNY	Dec. 31, 2013 CNY	Dec. 31, 2012 CNY	Dec. 31, 2014 Parent Company [Member] USD ($)	Dec. 31, 2014 Parent Company [Member] CNY	Dec. 31, 2013 Parent Company [Member] CNY	Dec. 31, 2012 Parent Company [Member] CNY
Operating expenses:
General and administrative expenses	$ (20,912)us-gaap_GeneralAndAdministrativeExpense	(129,751)us-gaap_GeneralAndAdministrativeExpense	(82,529)us-gaap_GeneralAndAdministrativeExpense	(83,153)us-gaap_GeneralAndAdministrativeExpense	$ (1,479)	(9,178)	(1,125)	(14,638)
Operating Profit(losses)	145,736us-gaap_OperatingIncomeLoss	904,235us-gaap_OperatingIncomeLoss	554,904us-gaap_OperatingIncomeLoss	298,466us-gaap_OperatingIncomeLoss	(1,479)	(9,178)	(1,125)	(14,638)
Interest income	5,590	34,682	11,082	5,093	802	4,973	0	0
Equity in income of subsidiaries					121,342	752,885	457,287	227,519
Income before income taxes	151,736	941,461	568,456	303,869	120,665	748,680	456,162	212,881
Income tax expense	31,071us-gaap_IncomeTaxExpenseBenefit	192,781us-gaap_IncomeTaxExpenseBenefit	112,294us-gaap_IncomeTaxExpenseBenefit	90,988us-gaap_IncomeTaxExpenseBenefit	0	0	0	0
Net income	120,665us-gaap_NetIncomeLoss	748,680us-gaap_NetIncomeLoss	456,162us-gaap_NetIncomeLoss	212,881us-gaap_NetIncomeLoss	120,665	748,680	456,162	212,881
Other comprehensive income, net of tax of nil
Foreign currency translation adjustments	636	3,946	1,403	583	636	3,946	1,734	252
Comprehensive income	$ 121,301us-gaap_ComprehensiveIncomeNetOfTax	752,626us-gaap_ComprehensiveIncomeNetOfTax	457,565us-gaap_ComprehensiveIncomeNetOfTax	213,464us-gaap_ComprehensiveIncomeNetOfTax	$ 121,301	752,626	457,896	213,133

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Interest income derived from funds deposited with both domestic and foreign financial institutions including funds in money market and other accounts.

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