Interest Income And Interest Expense (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest Income And Interest Expense [Abstract]
Investment securities									$ 71,526	$ 62,155	$ 45,946
Bank loans, net of unearned income									71,167	38,608	28,595
Margin balances									19,095	18,222	19,079
Other									24,181	23,554	15,085
Total interest income									185,969	142,539	108,705
Senior notes									26,617	20,648	11,777
Bank deposits									7,926	11,775	15,013
Other									6,718	13,945	6,580
Total interest expense	$ 12,560	$ 11,228	$ 8,842	$ 8,631	$ 11,630	$ 11,535	$ 12,634	$ 10,569	$ 41,261	$ 46,368	$ 33,370