Interest Income And Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Interest Income Expense Net [Abstract]
Bank loans, net	$ 48,729	$ 29,475	$ 93,489	$ 56,033
Investment securities	46,385	24,446	88,051	46,807
Margin balances	9,022	8,151	17,205	16,697
Inventory	4,346	4,519	8,582	9,017
Other	469	(811)	2,577	53
Total interest income	108,951	65,780	209,904	128,607
Senior notes	8,140	8,179	16,280	16,354
Bank deposits	1,887	1,842	3,654	3,743
Federal Home Loan Bank advances	2,797	2,635	4,516	3,392
Other	3,820	4,606	8,090	7,884
Total interest expense	$ 16,644	$ 17,262	$ 32,540	$ 31,373