Acquisitions (Details) - Narrative $ in Thousands				3 Months Ended	12 Months Ended
	Jan. 06, 2017 USD ($) location	Mar. 08, 2016 USD ($) location	Dec. 03, 2015 USD ($) location	Dec. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Business Acquisition [Line Items]
Goodwill				$ 340,879	$ 340,879	$ 319,007	$ 310,589	$ 264,062
Acquisition and integration related expenses					14,352	$ 1,389	$ 13,872
Standard Bancshares, Inc.
Business Acquisition [Line Items]
Acquisition and integration related expenses					8,000
Standard Bancshares, Inc. | Subsequent Event
Business Acquisition [Line Items]
Number of retail branches acquired | location	35
Total assets	$ 2,638,827
Total deposits	2,024,055
Loans	1,795,562
Consideration transferred	580,483
Goodwill	$ 328,296
NI Bancshares Corporation
Business Acquisition [Line Items]
Number of retail branches acquired | location		10
Total assets		$ 678,276
Total deposits		594,921
Loans		396,886
Minimum value of trust assets under management acquired		700,000
Consideration transferred		70,082
Goodwill		$ 21,751
Adjustment to goodwill				$ 1,000
Peoples Bancorp, Inc.
Business Acquisition [Line Items]
Number of retail branches acquired | location			2
Total assets			$ 110,513
Total deposits			91,813
Loans			53,766
Consideration transferred			16,828
Goodwill			$ 7,665
Adjustment to goodwill					$ 121