Securitizations and Variable Interest Entities - Unconsolidated VIEs with Significant Continuing Involvement (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Maximum Exposure to Loss	$ 6,000
Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	940,916	$ 50,523
Carrying Value, Net Assets	62,935	10,122
Maximum Exposure to Loss	63,535	10,122
Securities Available for Sale | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	47,049
Maximum Exposure to Loss	47,049
Accrued Interest Receivable | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	407
Maximum Exposure to Loss	407
Other Assets | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	15,779	10,122
Maximum Exposure to Loss	15,779	10,122
Accrued Expenses and Other Liabilities | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	(300)
Maximum Exposure to Loss	300
Securitizations | Accrued Expenses and Other Liabilities | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	(300)
Maximum Exposure to Loss	300
CLUB Certificates | Accrued Expenses and Other Liabilities | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0
Maximum Exposure to Loss	0
Investment funds | Accrued Expenses and Other Liabilities | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Liabilities	0
Maximum Exposure to Loss	0
Securitizations | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	863,589
Carrying Value, Net Assets	50,793
Maximum Exposure to Loss	51,393
Securitizations | Securities Available for Sale | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	45,256
Maximum Exposure to Loss	45,256
Securitizations | Accrued Interest Receivable | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	391
Maximum Exposure to Loss	391
Securitizations | Other Assets | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	5,446
Maximum Exposure to Loss	5,446
CLUB Certificates | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	36,833
Carrying Value, Net Assets	2,124
Maximum Exposure to Loss	2,124
CLUB Certificates | Securities Available for Sale | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	1,793
Maximum Exposure to Loss	1,793
CLUB Certificates | Accrued Interest Receivable | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	16
Maximum Exposure to Loss	16
CLUB Certificates | Other Assets | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	315
Maximum Exposure to Loss	315
Investment funds | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	40,494	50,523
Carrying Value, Net Assets	10,018	10,122
Maximum Exposure to Loss	10,018	10,122
Investment funds | Securities Available for Sale | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	0
Maximum Exposure to Loss	0
Investment funds | Accrued Interest Receivable | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	0
Maximum Exposure to Loss	0
Investment funds | Other Assets | Unconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying Value, Assets	10,018	10,122
Maximum Exposure to Loss	$ 10,018	$ 10,122