Valuation (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Valuation [Abstract]
Senior notes, estimated fair value					$ 86,000
Assets, Transfers out of Level 3				$ (51,600)
Assets, Transfers into Level 3				3,100
Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in unrealized gains (losses)	$ 5,700		$ 6,100
Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in unrealized gains (losses)	3,800		6,000
Investment in unconsolidated entities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in unrealized gains (losses)	2,000		(200)
Financial Derivatives - Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in unrealized gains (losses)	(56)		(300)
Other secured borrowings, at fair value
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in unrealized gains (losses)	(17)		40
Level 3
Valuation [Abstract]
Assets, Transfers out of Level 3	13,450	$ (51,604)	6,424	(44,487)
Assets, Transfers into Level 3	15,320	3,073	24,384	9,301
Level 3 | Investment in unconsolidated entities
Valuation [Abstract]
Assets, Transfers out of Level 3	0		0
Assets, Transfers into Level 3	$ 0		$ 0
Level 3 | Financial Derivatives - Assets
Valuation [Abstract]
Assets, Transfers out of Level 3		0		0
Assets, Transfers into Level 3		0		0
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in unrealized gains (losses)		(500)		(500)
Level 3 | Other secured borrowings, at fair value
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in unrealized gains (losses)		$ 400		$ 1,200