Acquisitions (Narrative) (Details) $ in Thousands, shares in Millions										12 Months Ended
	Dec. 06, 2019 USD ($)	Nov. 01, 2019 USD ($)	Sep. 27, 2019 USD ($)	Sep. 03, 2019 USD ($)	Jul. 01, 2019 USD ($)	Jan. 02, 2019 USD ($)	Oct. 01, 2018 USD ($)	Aug. 31, 2018 USD ($) shares	Mar. 19, 2018 USD ($) ClientAdvisor State	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill										$ 1,194,074	$ 1,034,679	$ 1,034,679
Institutional Group [Member]
Business Acquisition [Line Items]
Goodwill										849,093		694,284
Global Wealth Management [Member]
Business Acquisition [Line Items]
Goodwill										344,981		$ 340,395
GMP Capital Inc. [Member]
Business Acquisition [Line Items]
Date of acquisition	Dec. 06, 2019
GMP Capital Inc. [Member] | Institutional Group [Member]
Business Acquisition [Line Items]
Goodwill	$ 30,500
MainFirst Bank AG [Member]
Business Acquisition [Line Items]
Date of acquisition		Nov. 01, 2019
MainFirst Bank AG [Member] | Tradename, Non-Compete Agreements and Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets		$ 800
MainFirst Bank AG [Member] | Institutional Group [Member]
Business Acquisition [Line Items]
Goodwill		$ 14,600
George K. Baum & Company [Member]
Business Acquisition [Line Items]
Date of acquisition			Sep. 27, 2019
George K. Baum & Company [Member] | Customer Relationships and Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Identifiable intangible assets			$ 15,200
George K. Baum & Company [Member] | Institutional Group [Member]
Business Acquisition [Line Items]
Goodwill			$ 33,300
B&F Capital Markets, Inc. [Member]
Business Acquisition [Line Items]
Date of acquisition				Sep. 03, 2019
Period of contingent consideration				5 years
Liability for earn-out payments										20,100
B&F Capital Markets, Inc. [Member] | Tradename, Non-Compete Agreements and Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets				$ 18,600
B&F Capital Markets, Inc. [Member] | Institutional Group [Member]
Business Acquisition [Line Items]
Goodwill				$ 21,200
Mooreland Partners [Member]
Business Acquisition [Line Items]
Date of acquisition					Jul. 01, 2019
Period of contingent consideration					3 years
Liability for earn-out payments										18,400
Mooreland Partners [Member] | Non-Compete Agreements and Backlog [Member]
Business Acquisition [Line Items]
Identifiable intangible assets					$ 5,000
Mooreland Partners [Member] | Institutional Group [Member]
Business Acquisition [Line Items]
Goodwill					$ 51,000
First Empire Holding Corp. [Member]
Business Acquisition [Line Items]
Date of acquisition						Jan. 02, 2019
First Empire Holding Corp. [Member] | Tradename and Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets						$ 7,800
First Empire Holding Corp. [Member] | Institutional Group [Member]
Business Acquisition [Line Items]
Goodwill						$ 14,900
Rand & Associates [Member]
Business Acquisition [Line Items]
Period of contingent consideration							5 years
Liability for earn-out payments										$ 4,400	$ 4,100
Rand & Associates [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets							$ 4,700
Rand & Associates [Member] | Global Wealth Management [Member]
Business Acquisition [Line Items]
Goodwill							$ 9,300
Business Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Date of acquisition								Aug. 31, 2018
Business acquisition, equity interest issued or issuable, description										Under the terms of the merger agreement, each outstanding share of BBI common stock (except for shares of BBI common stock held by BBI as treasury stock) were converted into the right to receive 0.705 shares of our company’s common stock, with fractional shares settled with cash.
Business combination equity interest exchange ratio								0.705
Shares issued for acquisition | shares								2.0
Acquisition of loans								$ 507,800
Acquisition of other assets								85,700
Acquisition of deposits								501,100
Acquisition of other liabilities								21,900
Business Bancshares, Inc. [Member] | Core Deposits [Member]
Business Acquisition [Line Items]
Identifiable intangible assets								8,600
Business Bancshares, Inc. [Member] | Global Wealth Management [Member]
Business Acquisition [Line Items]
Goodwill								$ 41,600
Ziegler [Member]
Business Acquisition [Line Items]
Date of acquisition									Mar. 19, 2018
Goodwill									$ 19,000
Number of private client advisors | ClientAdvisor									55
Number of states in which private client advisors operates | State									5
Assets									$ 5,000,000
Ziegler [Member] | Customer Relationships and Non-Compete Agreements [Member]
Business Acquisition [Line Items]
Identifiable intangible assets									$ 9,500