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Segregated Cash	12 Months Ended
Segregated Cash	Dec. 31, 2017
Segregated Cash [Abstract]
Restricted Assets Disclosure [Text Block]	Segregated Cash As of December 31, 2017 and 2016, cash segregated in compliance with federal regulations and other restricted deposits of $116.3 million and $1.0 million, respectively, consisted of cash deposited in special bank accounts for the benefit of customers under SEC Rule 15c3-3 and cash held in accounts designated as Special Reserve Bank Accounts for Proprietary Accounts of Broker-Dealers ("PAB").