Discontinued Operations, Assets and Liabilities Held for Sale & Sales of Businesses - Income Disclosures (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]
Revenues and gain (adjustment to gain) on sale	$ 39,868		$ (1,148)
Expenses:
Compensation	14,068		70
Payments for order flow	9,885		0
Execution and clearance fees	5,038		0
Other expenses	10,748		930
Total expenses	39,739		1,000
Pre-tax (loss) income from discontinued operations	129		(2,148)
Income tax expense (benefit)	49		(816)
(Loss) income from discontinued operations, net of tax	$ 80	$ 0	$ (1,332)	$ 80