Dealer Finance Receivables accretable yield (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Accretable Yield [Roll Forward]
Balance, Beginning of Period	$ 8,887	$ 0
Accretion (Revenue Recognized)	(2,037)	(125)
Additions	9,999	1,792
Reclassification from (to) Nonaccretable Yield	0	0
Balance, End of Period	$ 16,849	$ 1,667

The change in the estimate of cash flows expected to be collected, after origination of loans, which results in an increase in accretable yield (for example, if actual cash flows are significantly greater than previously expected). This relates to loans originated through our indirect lending activities, for which it is probable, at origination, that the company will be unable to collect all contractually required payments receivable.

No definition available.

Name:	dta_ReclassificationsOfAccretableYield
Namespace Prefix:	dta_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration