Debt (Narrative) (Details) - USD ($)					6 Months Ended
		Mar. 30, 2015	Feb. 21, 2014	Jan. 22, 2014	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Debt Instrument [Line Items]
Maximum hedging reserve					$ 1,000,000
Debt facility financing amount					$ 2,557,400,000		$ 2,086,300,000
Percentage of collections on contributed loans					6.00%
Monthly servicing fee per financing					6.00%
Proceeds from issuance of senior notes					$ 0	$ 248,200,000
Debt covenants					1
Unamortized debt discount					1,600,000		1,700,000
Revolving Secured Line of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility					$ 310,000,000
Percentage of net book value of loans					0.00%
Debt facility financing amount	[1]				$ 0		57,700,000
Wholly-owned Subsidiary					n/a
Unamortized debt discount	[1]				$ 0		$ 0
Warehouse Facilities [Member]
Debt Instrument [Line Items]
Percentage of net book value of loans					80.00%
Number of warehouse facilities					4
Debt facility financing amount					$ 650,000,000
Warehouse Facility II [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2],[3]				$ 400,000,000
Wholly-owned Subsidiary	[2]				CAC Warehouse Funding Corp. II
Debt maturity date	[2],[4]				Jun. 23, 2019
Senior notes yield to maturity					0.00%		0.00%
Warehouse Facility IV [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2],[3]				$ 75,000,000
Wholly-owned Subsidiary	[2]				CAC Warehouse Funding LLC IV
Debt maturity date	[2],[4]				Apr. 30, 2018
Senior notes yield to maturity					2.46%		2.42%
Warehouse Facility V [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2],[3]				$ 100,000,000
Wholly-owned Subsidiary	[2]				CAC Warehouse Funding LLC V
Debt maturity date	[2],[5]				Sep. 10, 2017
Senior notes yield to maturity					0.00%		0.00%
Warehouse Facility VI [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]				$ 75,000,000
Wholly-owned Subsidiary	[2]				CAC Warehouse Funding LLC VI
Debt maturity date	[2],[4]				Sep. 30, 2018
Senior notes yield to maturity					0.00%		2.24%
2017 Senior Notes [Member]
Debt Instrument [Line Items]
Senior notes stated interest rate			9.125%
Repayment of senior notes			$ 350,000,000
2021 Senior Notes [Member]
Debt Instrument [Line Items]
Debt facility financing amount				$ 300,000,000	$ 300,000,000
Wholly-owned Subsidiary					n/a
Close date, secured financings				Jan. 22, 2014
Senior notes stated interest rate				6.125%
Debt maturity date				Feb. 15, 2021	Feb. 15, 2021
Senior notes yield to maturity					6.125%		6.125%
2023 Senior Notes [Member]
Debt Instrument [Line Items]
Debt facility financing amount		$ 250,000,000.0			$ 250,000,000
Wholly-owned Subsidiary					n/a
Close date, secured financings		Mar. 30, 2015
Senior notes stated interest rate		7.375%
Debt maturity date		Mar. 15, 2023			Mar. 15, 2023
Redemption price, percentage of principal amount redeemed		99.266%
Proceeds from issuance of senior notes		$ 248,200,000
Senior notes yield to maturity		7.50%			7.375%		7.375%
Term ABS 2013-1 [Member]
Debt Instrument [Line Items]
Debt maturity date					Apr. 15, 2015
Senior notes yield to maturity					0.00%		1.56%
Term ABS 2013-2 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]				$ 197,800,000.0
Wholly-owned Subsidiary	[2]				Credit Acceptance Funding LLC 2013-2
Debt financing close date					Oct. 31, 2013
Debt maturity date	[2],[4]				Oct. 15, 2015
Senior notes yield to maturity					2.03%		1.71%
Term ABS 2014-1 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]				$ 299,000,000
Wholly-owned Subsidiary	[2]				Credit Acceptance Funding LLC 2014-1
Debt financing close date					Apr. 16, 2014
Debt maturity date	[2],[4]				Apr. 15, 2016
Senior notes yield to maturity					1.75%		1.72%
Term ABS 2014-2 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]				$ 349,000,000.0
Wholly-owned Subsidiary	[2]				Credit Acceptance Funding LLC 2014-2
Debt financing close date					Sep. 25, 2014
Debt maturity date	[2],[4]				Sep. 15, 2016
Senior notes yield to maturity					2.05%		2.05%
Term ABS 2015-1 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]				$ 300,600,000
Wholly-owned Subsidiary	[2]				Credit Acceptance Funding LLC 2015-1
Debt financing close date					Jan. 29, 2015
Debt maturity date	[2],[4]				Jan. 16, 2017
Senior notes yield to maturity					2.26%		2.26%
Term ABS 2015-2 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]				$ 300,200,000
Wholly-owned Subsidiary	[2]				Credit Acceptance Funding LLC 2015-2
Debt financing close date					Aug. 20, 2015
Debt maturity date	[2],[4]				Aug. 15, 2017
Senior notes yield to maturity					2.63%		2.63%
Term ABS 2016-1 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]				$ 385,000,000
Wholly-owned Subsidiary	[2]				Credit Acceptance Funding LLC 2016-1
Debt financing close date					Feb. 26, 2016
Debt maturity date	[2],[4]				Feb. 15, 2018
Senior notes yield to maturity					2.39%
Term ABS 2016-2 [Member]
Debt Instrument [Line Items]
Debt facility financing amount	[2]				$ 350,200,000
Wholly-owned Subsidiary	[2]				Credit Acceptance Funding LLC 2016-2
Debt financing close date					May 12, 2016
Debt maturity date	[2],[4]				May 15, 2018
Senior notes yield to maturity					2.83%

[1] Excludes deferred debt issuance costs of $2.9 million and $2.2 million as of June 30, 2016 and December 31, 2015, respectively, which are included in other assets.

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

[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 maturity date based on the cash flows of the pledged assets.

[5] 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.