Variable Interest Entities - Additional Disclosures (Details) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2014 USD ($) VIE	Dec. 31, 2013 USD ($)	Sep. 30, 2014 VIE
Variable Interest Entity [Line Items]
Number of variable interest entities formed | VIE			3
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Income earned by VIEs	$ 10.6	$ 2.2
VIE expenses	$ 11.0	$ 0.7
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Number of VIEs | VIE	2
Grupo Finmart [Member] | VIE C and B [Member]
Variable Interest Entity [Line Items]
Percent of cash flows received from VIE	100.00%
Grupo Finmart [Member] | VIE A [Member]
Variable Interest Entity [Line Items]
Percent of cash flows received from VIE	50.00%