Acquisitions (Narrative) (Details) $ in Thousands				3 Months Ended	9 Months Ended
	Jul. 07, 2017 USD ($) building shares	Feb. 28, 2017 USD ($) building shares	Feb. 05, 2016 USD ($) shares	Jun. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)
Business Acquisition [Line Items]
Assets					$ 9,755,627	$ 8,247,079	$ 8,202,215
Loans outstanding					6,318,530	5,297,395
Deposits					8,231,884	6,847,411
Goodwill					236,615	127,699
Nonaccrual loans					59,451	$ 62,591
Citywide Banks
Business Acquisition [Line Items]
Purchase price	$ 211,243
Purchase price in cash	$ 58,636
Purchase price paid by delivery of shares of common stock (in shares) | shares	3,216,161
Assets	$ 1,490,000
Loans outstanding	985,400
Deposits	1,210,000
Goodwill	$ 95,154
Merger related expenses					3,800
Nonaccrual loans					$ 1,100
Number of bank buildings sold (building) | building	1
Fair value of buildings sold	$ 1,400
Stock issued	152,607
Other borrowings	$ 21,636
Citywide Banks | Common Stock
Business Acquisition [Line Items]
Purchase price paid by delivery of shares of common stock (in shares) | shares	3,216,161
Founders Bancorp
Business Acquisition [Line Items]
Purchase price		$ 31,000
Purchase price in cash		$ 8,400
Purchase price paid by delivery of shares of common stock (in shares) | shares		455,877
Assets		$ 213,900
Deposits		181,500
Goodwill		13,800
Loans		$ 96,400
Number of bank buildings sold (building) | building		1
Fair value of buildings sold				$ 576
Founders Bancorp | Common Stock
Business Acquisition [Line Items]
Purchase price paid by delivery of shares of common stock (in shares) | shares		455,877
CIC Bancshares, Inc.
Business Acquisition [Line Items]
Purchase price			$ 76,900
Purchase price in cash			$ 15,700
Purchase price paid by delivery of shares of common stock (in shares) | shares			2,003,235
Assets			$ 772,600
Deposits			648,100
Goodwill			29,800
Loans			581,500
Other borrowings			7,900
CIC Bancshares, Inc. | Preferred Stock
Business Acquisition [Line Items]
Stock issued			$ 3,800
CIC Bancshares, Inc. | Common Stock
Business Acquisition [Line Items]
Purchase price paid by delivery of shares of common stock (in shares) | shares			2,003,235