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Share-Based Compensation - Summary of Stock Options Granted to Employees and Directors (Parenthetical) (Detail) (Employee Stock Option [Member], Directors and Employees [Member], 2011 Plan [Member])	0 Months Ended	12 Months Ended	0 Months Ended
	Oct. 22, 2013	Dec. 31, 2014	Jul. 01, 2012	May 27, 2013	Jan. 16, 2014
October 22, 2013 [Member] | Options Grant October Date Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		25% of the awards have vested on July 1, 2014 and the remainder of the awards will vest on an annual basis each July 1, thereafter, until July 1, 2017.
Percentage of awards vesting	25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardDateAxis = athm_OctoberTwentySecondTwoThousandThirteenMember / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = athm_TwoThousandAndElevenPlanMember / us-gaap_TitleOfIndividualAxis = athm_DirectorsAndEmployeesMember / us-gaap_VestingAxis = athm_OptionsGrantOctoberDateTwoMember
October 22, 2013 [Member] | Options Grant October Date One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		25% of the awards have vested on January 1, 2014 and the remainder of the awards will vest on an annual basis each January 1, thereafter, until January 1, 2017.
Percentage of awards vesting	25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardDateAxis = athm_OctoberTwentySecondTwoThousandThirteenMember / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = athm_TwoThousandAndElevenPlanMember / us-gaap_TitleOfIndividualAxis = athm_DirectorsAndEmployeesMember / us-gaap_VestingAxis = athm_OptionsGrantOctoberDateOneMember
July 1, 2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		25% of the awards have vested on each of July 1, 2013 and 2014 and the remainder of the awards will vest on an annual basis each July 1, thereafter, until July 1, 2016.
Percentage of awards vesting			25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardDateAxis = athm_JulyFirstTwoThousandTwelveMember / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = athm_TwoThousandAndElevenPlanMember / us-gaap_TitleOfIndividualAxis = athm_DirectorsAndEmployeesMember
May 27, 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		25% of the awards have vested on January 1, 2014 and the remainder of the awards will vest on an annual basis each January 1, thereafter, until January 1, 2017.
Percentage of awards vesting				25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardDateAxis = athm_MayTwentySevenTwoThousandThirteenMember / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = athm_TwoThousandAndElevenPlanMember / us-gaap_TitleOfIndividualAxis = athm_DirectorsAndEmployeesMember
January 16, 2014 [Member] | Options Grant January Date One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		25% of the awards have vested on January 16, 2014 and the remainder of the awards will vest on an annual basis each January 16, thereafter, until January 16, 2017.
Percentage of awards vesting					25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardDateAxis = athm_JanuarySixteenTwoThousandFourteenMember / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = athm_TwoThousandAndElevenPlanMember / us-gaap_TitleOfIndividualAxis = athm_DirectorsAndEmployeesMember / us-gaap_VestingAxis = athm_OptionsGrantJanuaryDateOneMember
January 16, 2014 [Member] | Options Grant January Date Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		25% of the awards will vest on January 1, 2015 and the remainder of the awards will vest on an annual basis each January 1, thereafter, until January 1, 2018.
Percentage of awards vesting					25.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardDateAxis = athm_JanuarySixteenTwoThousandFourteenMember / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = athm_TwoThousandAndElevenPlanMember / us-gaap_TitleOfIndividualAxis = athm_DirectorsAndEmployeesMember / us-gaap_VestingAxis = athm_OptionsGrantJanuaryDateTwoMember

X

- Definition

Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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X

- Definition

Percentage of vesting of share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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