Mergers and Acquisitions - Narrative (Details) $ in Thousands	Jul. 01, 2017 USD ($) branch shares	Apr. 01, 2016 USD ($) branch shares	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)
Business Acquisition [Line Items]
Goodwill resulting from merger			$ 611,046	$ 470,534	$ 470,534
Metropolitan Bancgroup, Inc.
Business Acquisition [Line Items]
Transaction value	$ 219,461
Shares issued to common shareholders (shares) | shares	4,883,182
Cash settlement for stock options	$ 4,764
Voting interest acquired (percent)	100.00%
Number of locations acquired | branch	8
Intangible assets, including goodwill	$ 147,478
Goodwill resulting from merger	140,512
Core deposit intangible	$ 6,966
Weighted average useful life (in years)	10 years
Assets acquired	$ 78,949
KeyWorth Bank
Business Acquisition [Line Items]
Transaction value		$ 58,884
Voting interest acquired (percent)		100.00%
Intangible assets, including goodwill		$ 22,643
Goodwill resulting from merger		20,633
Core deposit intangible		$ 2,010
Weighted average useful life (in years)		10 years
Payment to stock option holders		$ 3,594
Assets acquired		415,232
Recognized identifiable assets acquired and liabilities assumed, financial assets		$ 272,330
Number of offices in operation | branch		6
KeyWorth Bank | Core Deposits
Business Acquisition [Line Items]
Deposits		$ 348,961
KeyWorth Bank | Common Stock
Business Acquisition [Line Items]
Shares issued to common shareholders (shares) | shares		1,680,021