Acquisitions - Narrative (Details) $ in Thousands				3 Months Ended		6 Months Ended
	Jun. 28, 2016 USD ($) location	Mar. 08, 2016 USD ($) location	Dec. 03, 2015 USD ($) location	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)
Business Acquisition [Line Items]
Acquisition and integration related expenses				$ 618	$ 0	$ 5,638	$ 0
Standard Bancshares, Inc.
Business Acquisition [Line Items]
Announced number of locations to be acquired | location	35
Announced assets to be acquired	$ 2,500,000
Announced deposits to be acquired	2,200,000
Announced loans to be acquired	$ 1,800,000
Announced fixed exchange ratio	0.4350
Announced consideration to be transferred	$ 365,000
NI Bancshares Corporation
Business Acquisition [Line Items]
Number of retail branches acquired | location		10
Minimum value of trust assets under management acquired		$ 700,000
Consideration transferred		70,082
Goodwill		$ 20,762
Peoples Bancorp, Inc.
Business Acquisition [Line Items]
Number of retail branches acquired | location			2
Consideration transferred			$ 16,828
Goodwill			$ 7,544