Acquisitions and Divestitures - Acquisitions Narrative (Details) $ / shares in Units, $ in Thousands				12 Months Ended
	Dec. 31, 2015 USD ($) bank_branch shares	Apr. 17, 2015 USD ($) bank_branch $ / shares	Nov. 07, 2014 USD ($) bank_branch $ / shares shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares
Business Acquisition [Line Items]
Value of stock issued as a part of acquisition					$ 70,402	$ 34,981
Cash paid in acquisition					14,500	$ 14,208
Pro forma nonrecurring expense					$ 12,000
Common Stock
Business Acquisition [Line Items]
Stock issued as a part of acquisition (in shares) | shares					2,769,568	1,574,298
Value of stock issued as a part of acquisition					$ 346	$ 197
Merger with Ameriana Bancorp
Business Acquisition [Line Items]
Percentage of interest acquired	100.00%				100.00%
Number of banking centers acquired | bank_branch	13
Stock issued as a part of acquisition (in shares) | shares	2,800,000
Value of stock issued as a part of acquisition	$ 70,400
Core deposit intangible	$ 5,342				$ 5,342
Acquired intangible asset, expected useful life	10 years
Total purchase price	$ 70,402				$ 70,402
Merger with Ameriana Bancorp | Common Stock
Business Acquisition [Line Items]
Number of shares of common stock	0.9037				0.9037
Merger with C Financial Corporation
Business Acquisition [Line Items]
Percentage of interest acquired		100.00%
Number of banking centers acquired | bank_branch		6
Core deposit intangible		$ 981
Acquired intangible asset, expected useful life		10 years
Total purchase price		$ 14,500
Cash received by shareholders for each share of common stock held (in dollars per share) | $ / shares		$ 6.738
Merger with Community Bancshares, Inc.
Business Acquisition [Line Items]
Percentage of interest acquired			100.00%
Number of banking centers acquired | bank_branch			10
Stock issued as a part of acquisition (in shares) | shares			1,600,000
Value of stock issued as a part of acquisition			$ 35,000
Core deposit intangible			$ 4,658
Acquired intangible asset, expected useful life			10 years
Total purchase price			$ 49,189
Share price (in dollars per share) | $ / shares			$ 85.94
Cash paid in acquisition			$ 14,200
Pro forma nonrecurring expense						1,800
Pro forma revenue						$ 1,600
Merger with Community Bancshares, Inc. | Common Stock
Business Acquisition [Line Items]
Number of shares of common stock			4.0926