Securitization and Variable Interest Entities - Unconsolidated VIEs with Significant Continuing Involvement (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 6,000
Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	84,291	$ 63,535
Carrying Value, Assets	1,315,922	940,916
Carrying Value, Net Assets	84,291	62,935
Securitizations | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	63,835	51,393
Carrying Value, Assets	1,087,108	863,589
Carrying Value, Net Assets	63,835	50,793
CLUB Certificates | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	11,507	2,124
Carrying Value, Assets	192,565	36,833
Carrying Value, Net Assets	11,507	2,124
Investment Fund | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	8,949	10,018
Carrying Value, Assets	36,249	40,494
Carrying Value, Net Assets	8,949	10,018
Securities Available for Sale | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	66,010	47,049
Carrying Value, Assets	66,010	47,049
Securities Available for Sale | Securitizations | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	56,232	45,256
Carrying Value, Assets	56,232	45,256
Securities Available for Sale | CLUB Certificates | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	9,778	1,793
Carrying Value, Assets	9,778	1,793
Securities Available for Sale | Investment Fund | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	0	0
Carrying Value, Assets	0	0
Accrued Interest Receivable | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	789	407
Carrying Value, Assets	789	407
Accrued Interest Receivable | Securitizations | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	738	391
Carrying Value, Assets	738	391
Accrued Interest Receivable | CLUB Certificates | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	51	16
Carrying Value, Assets	51	16
Accrued Interest Receivable | Investment Fund | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	0	0
Carrying Value, Assets	0	0
Other Assets | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	17,492	15,779
Carrying Value, Assets	17,492	15,779
Other Assets | Securitizations | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	6,865	5,446
Carrying Value, Assets	6,865	5,446
Other Assets | CLUB Certificates | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	1,678	315
Carrying Value, Assets	1,678	315
Other Assets | Investment Fund | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	8,949	10,018
Carrying Value, Assets	8,949	10,018
Accrued Expenses and Other Liabilities | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	0	300
Carrying Value, Liabilities	0	(300)
Securitizations | Accrued Expenses and Other Liabilities | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	0	300
Carrying Value, Liabilities	0	(300)
CLUB Certificates | Accrued Expenses and Other Liabilities | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	0	0
Carrying Value, Liabilities	0	0
Investment Fund | Accrued Expenses and Other Liabilities | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	0	0
Carrying Value, Liabilities	$ 0	$ 0