Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			0 Months Ended		1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 20, 2012	Feb. 15, 2013	Nov. 30, 2013	Jul. 31, 2014	Dec. 31, 2014
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Number of shares authorized to be repurchased	3,500,000							3,500,000
Shares issued during the period	2,600,000	8,800,000	2,300,000
Common stock reissued		500,000	2,100,000
Treasury Stock Acquired, Average Cost Per Share	$ 31.75	$ 30.35
Treasury Stock, Shares, Acquired	400,000	400,000
Treasury Stock, Value, Acquired, Cost Method		$ 13,670	$ 11,380
Miller Buckfire & Co. LLC [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issuance of common stock for acquisitions, Shares				100,000
KBW [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issuance of common stock for acquisitions, Shares					6,700,000
Ziegler Lotsoff Capital Management, LLC [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issuance of common stock for acquisitions, Shares						100,000
Ouriel Securities [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issuance of common stock for acquisitions, Shares							300,000
Merchant Capital LLC [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issuance of common stock for acquisitions, Shares								100,000