Receivables and Payables (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Receivables from brokers, dealers and clearing organizations
Broker-dealers	$ 200,073		$ 167,514
Clearing organizations	11,172		3,480
Securities borrowed	763,613		866,520
Allowance for doubtful accounts	(425)		(737)
Total	974,433		1,036,777
Payables to brokers, dealers and clearing organizations
Broker-dealers	73,779		64,763
Clearing organizations	3,283		7,644
Securities loaned	820,461		888,152
Total	897,523		960,559
Receivables from customers
Customers	70,836		49,688
Allowance for doubtful accounts	(685)		(512)
Total	70,151		49,176
Payables to customers
Customers	21,026		9,957
Total	21,026		9,957
Securities Borrowed and Loaned
Fair value of securities borrowed	799,000
Interest earned	1,632	$ 1,408
Interest incurred	(1,066)	(1,046)
Interest earned (incurred), net	566	$ 362
Deposits paid for securities borrowed
Gross Amounts of Recognized Assets	763,613		866,520
Net Amounts Presented in the Consolidated Statement of Financial Condition	763,613		866,520
Collateral Received or Pledged (including Cash)	763,613		866,520
Deposits received for securities loaned
Gross Amounts of Recognized Liabilities	(820,461)		(888,152)
Net Amounts Presented in the Consolidated Statement of Financial Condition	(820,461)		(888,152)
Collateral Received or Pledged (including Cash)	(805,498)		(868,843)
Net Amount	$ (14,963)		$ (19,309)