Acquisitions (Narrative) (Details) - USD ($) $ in Thousands							3 Months Ended	12 Months Ended
	Oct. 07, 2015	Jun. 05, 2015	Nov. 07, 2014	Jul. 31, 2014	Feb. 15, 2013	Oct. 01, 2011	Mar. 31, 2016	Dec. 31, 2013	Dec. 31, 2015	Dec. 04, 2015	Dec. 31, 2014	Apr. 03, 2014	Nov. 30, 2013	Oct. 31, 2013
Business Acquisition [Line Items]
Goodwill									$ 915,602		$ 795,026
Bargain purchase gain								$ 7,566
Kelwynne, LLC [Member]
Business Acquisition [Line Items]
Date of acquisition	Oct. 07, 2015
Ownership percentage	40.00%
Barclays’ Wealth and Investment Management, Americas [Member]
Business Acquisition [Line Items]
Goodwill										$ 32,200
Deferred consideration, recognized as a liability										15,600
Barclays’ Wealth and Investment Management, Americas [Member] | Scenario, Forecast [Member] | Restricted Stock Units (RSUs) [Member]
Business Acquisition [Line Items]
Restricted stock units granted, shares							2,000,000
Restricted stock units granted, value							$ 60,000
Barclays’ Wealth and Investment Management, Americas [Member] | Stifel Bank [Member]
Business Acquisition [Line Items]
Loans acquired in acquisition										$ 600,000
Sterne Agee Group, Inc. [Member]
Business Acquisition [Line Items]
Goodwill and intangible assets		$ 90,100
Fair value of awards issued as retention		23,800
Employee retention compensation paid in notes		$ 33,800
Sterne Agee Group, Inc. [Member] | Minimum [Member]
Business Acquisition [Line Items]
Individual compensation and benefits useful period		5 years
Sterne Agee Group, Inc. [Member] | Maximum [Member]
Business Acquisition [Line Items]
Individual compensation and benefits useful period		10 years
Merchant Capital LLC [Member]
Business Acquisition [Line Items]
Goodwill											$ 17,900
1919 Investment Counsel And Trust Company NA [Member]
Business Acquisition [Line Items]
Goodwill			$ 11,600
Fair value of awards issued as retention			11,200
Employee retention compensation paid in notes			10,800
1919 Investment Counsel And Trust Company NA [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets			$ 6,100
Oriel Securities [Member]
Business Acquisition [Line Items]
Goodwill				$ 18,200
Fair value of awards issued as retention				6,800
Oriel Securities [Member] | Trade Name [Member]
Business Acquisition [Line Items]
Identifiable intangible assets				1,900
Oriel Securities [Member] | Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Identifiable intangible assets				$ 1,400
De La Rosa & Co. [Member]
Business Acquisition [Line Items]
Goodwill												$ 17,400
De La Rosa & Co. [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets												200
De La Rosa & Co. [Member] | Trade Name [Member]
Business Acquisition [Line Items]
Identifiable intangible assets												$ 1,800
Acacia Federal Savings Bank [Member]
Business Acquisition [Line Items]
Loans acquired in acquisition														$ 337,100
Other assets acquired														180,400
Deposits assumed														435,400
Other liabilities assumed														$ 10,000
Bargain purchase gain								$ 7,600
Ziegler Lotsoff Capital Management, LLC [Member]
Business Acquisition [Line Items]
Goodwill													$ 6,800
Ziegler Lotsoff Capital Management, LLC [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets													3,400
Ziegler Lotsoff Capital Management, LLC [Member] | Trade Name [Member]
Business Acquisition [Line Items]
Identifiable intangible assets													$ 100
KBW [Member]
Business Acquisition [Line Items]
Fair value of awards issued as retention					$ 30,600
Stone & Youngberg LLC [Member]
Business Acquisition [Line Items]
Consideration to be paid in installments						$ 24,000
Number of years in installment plan						3 years
Period of contingent consideration						5 years
Maximum earn-out						$ 25,000
Liability for earn-out payments									$ 9,300