Goodwill, Core Deposit Premium and Other Intangible Assets (Goodwill) (Narrative) (Details) - USD ($)		3 Months Ended
	Sep. 30, 2017	Mar. 31, 2018	Feb. 23, 2018	Dec. 31, 2017	Jul. 07, 2017	Feb. 28, 2017
Goodwill [Line Items]
Goodwill		$ 270,305,000		$ 236,615,000
Goodwill impairment	$ 0
Core Deposits
Goodwill [Line Items]
Intangibles, amortization period		10 years
Signature Bancshares, Inc.
Goodwill [Line Items]
Goodwill			$ 33,700,000
Signature Bancshares, Inc. | Core Deposits
Goodwill [Line Items]
Intangibles recognized			$ 7,700,000
Citywide Banks
Goodwill [Line Items]
Goodwill					$ 95,200,000
Citywide Banks | Core Deposits
Goodwill [Line Items]
Intangibles recognized					$ 16,000,000
Founders Bancorp
Goodwill [Line Items]
Goodwill						$ 13,800,000
Founders Bancorp | Core Deposits
Goodwill [Line Items]
Intangibles recognized						$ 2,500,000