4. Securitization Trust Debt (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
"Securitization trust debt," and components of debt
Receivables Pledged at end of period	$ 1,646,306
Initial Principal	2,879,200
Outstanding Principal	1,697,649	1,598,496
CPS 2011-A [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	April 2018
Receivables Pledged at end of period	10,138
Initial Principal	100,364
Outstanding Principal	5,836	8,457
Weighted Average Contractual Interest Rate end of period	2.82%
CPS 2011-B [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	September 2018
Receivables Pledged at end of period	19,613
Initial Principal	109,936
Outstanding Principal	19,299	22,985
Weighted Average Contractual Interest Rate end of period	4.46%
CPS 2011-C [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	March 2019
Receivables Pledged at end of period	25,918
Initial Principal	119,400
Outstanding Principal	26,049	30,601
Weighted Average Contractual Interest Rate end of period	4.92%
CPS 2012-A [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	June 2019
Receivables Pledged at end of period	31,274
Initial Principal	155,000
Outstanding Principal	30,393	35,923
Weighted Average Contractual Interest Rate end of period	3.35%
CPS 2012-B [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	September 2019
Receivables Pledged at end of period	44,458
Initial Principal	141,500
Outstanding Principal	43,388	50,125
Weighted Average Contractual Interest Rate end of period	3.06%
CPS 2012-C [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	December 2019
Receivables Pledged at end of period	49,655
Initial Principal	147,000
Outstanding Principal	48,610	55,619
Weighted Average Contractual Interest Rate end of period	2.40%
CPS 2012-D [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	March 2020
Receivables Pledged at end of period	60,076
Initial Principal	160,000
Outstanding Principal	59,229	67,833
Weighted Average Contractual Interest Rate end of period	2.06%
CPS 2013-A [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	June 2020
Receivables Pledged at end of period	87,361
Initial Principal	185,000
Outstanding Principal	87,059	97,775
Weighted Average Contractual Interest Rate end of period	1.95%
CPS 2013-B [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	September 2020
Receivables Pledged at end of period	106,376
Initial Principal	205,000
Outstanding Principal	106,305	118,692
Weighted Average Contractual Interest Rate end of period	2.44%
CPS 2013-C [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	December 2020
Receivables Pledged at end of period	122,248
Initial Principal	205,000
Outstanding Principal	120,830	133,628
Weighted Average Contractual Interest Rate end of period	2.87%
CPS 2013-D [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	March 2021
Receivables Pledged at end of period	120,330
Initial Principal	183,000
Outstanding Principal	118,794	132,150
Weighted Average Contractual Interest Rate end of period	2.54%
CPS 2014-A [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	June 2021
Receivables Pledged at end of period	132,426
Initial Principal	180,000
Outstanding Principal	130,422	143,456
Weighted Average Contractual Interest Rate end of period	2.13%
CPS 2014-B [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	September 2021
Receivables Pledged at end of period	166,835
Initial Principal	202,500
Outstanding Principal	165,346	177,601
Weighted Average Contractual Interest Rate end of period	1.92%
CPS 2014-C [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	December 2021
Receivables Pledged at end of period	244,750
Initial Principal	273,000
Outstanding Principal	241,176	256,151
Weighted Average Contractual Interest Rate end of period	2.15%
CPS 2014-D [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	March 2022
Receivables Pledged at end of period	254,224
Initial Principal	267,500
Outstanding Principal	249,913	267,500
Weighted Average Contractual Interest Rate end of period	2.40%
CPS 2015-A [Member]
"Securitization trust debt," and components of debt
Final Scheduled Payment Date	June 2022
Receivables Pledged at end of period	170,624
Initial Principal	245,000
Outstanding Principal	$ 245,000
Weighted Average Contractual Interest Rate end of period	2.31%