Debt (Schedule of General Information of Financing Transaction) (Details) - USD ($)				9 Months Ended
		Mar. 30, 2015	Jan. 22, 2014	Sep. 30, 2015		Jun. 11, 2015	May. 19, 2015
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary				n/a
Line of credit maturity date				Jun. 22, 2018
Financing Amount				$ 310,000,000		$ 235,000,000
Revolving Secured Line of Credit [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate				1.875%
Revolving Secured Line of Credit [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Basis spread on variable rate				0.875%
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding Corp. II
Debt maturity date	[1],[2]			Jul. 18, 2017
Debt facility financing amount				$ 400,000,000	[1],[3]		$ 325,000,000
Warehouse Facility II [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	[1],[2]			2.00%
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding LLC IV
Debt maturity date	[1],[2]			Apr. 30, 2018
Debt facility financing amount	[1],[3]			$ 75,000,000
Warehouse Facility IV [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	[1],[2]			2.00%
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding LLC V
Debt maturity date	[1],[4]			Sep. 10, 2017
Debt facility financing amount				$ 100,000,000	[1],[3]	$ 75,000,000
Warehouse Facility V [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	[1],[2]			1.60%
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			CAC Warehouse Funding LLC VI
Debt maturity date	[1],[2]			Sep. 30, 2018
Debt facility financing amount	[1]			$ 75,000,000
Warehouse Facility VI [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on variable rate	[1],[2]			2.00%
Term ABS 2013-1 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2013-1
Debt maturity date	[1],[2]			Apr. 15, 2015
Debt facility financing amount	[1]			$ 140,300,000.0
Term ABS 2013-2 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2013-2
Debt maturity date	[1],[2]			Oct. 15, 2015
Debt facility financing amount	[1]			$ 197,800,000.0
Term ABS 2014-1 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2014-1
Debt maturity date	[1],[2]			Apr. 15, 2016
Debt facility financing amount	[1]			$ 299,000,000
Term ABS 2014-2 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2014-2
Debt maturity date	[1],[2]			Sep. 15, 2016
Debt facility financing amount	[1]			$ 349,000,000.0
Term ABS 2015-1 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2015-1
Debt maturity date	[1],[2]			Jan. 16, 2017
Debt facility financing amount				$ 300,600,000
Term ABS 2015-2 [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary	[1]			Credit Acceptance Funding LLC 2015-2
Debt maturity date	[1],[2]			Aug. 15, 2017
Debt facility financing amount				$ 300,200,000
2021 Senior Notes [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary				n/a
Debt maturity date			Feb. 15, 2021	Feb. 15, 2021
Debt facility financing amount			$ 300,000,000	$ 300,000,000
2023 Senior Notes [Member]
Debt Instrument [Line Items]
Wholly-owned Subsidiary				n/a
Debt maturity date		Mar. 15, 2023		Mar. 15, 2023
Debt facility financing amount		$ 250,000,000.0		$ 250,000,000

[1] Financing made available only to a specified subsidiary of the Company.

[2] Represents the revolving maturity date. The outstanding balance will amortize after the maturity date based on the cash flows of the pledged assets.

[3] Interest rate cap agreements are in place to limit the exposure to increasing interest rates.

[4] Represents the revolving maturity date. The outstanding balance will amortize after the revolving maturity date and any amounts remaining on September 10, 2019 will be due.