Acquisitions and Divestitures - Narrative (Details) $ / shares in Units, $ in Thousands					12 Months Ended
	Dec. 31, 2015 USD ($) bank shares	Apr. 17, 2015 USD ($) bank $ / shares	Nov. 07, 2014 USD ($) bank $ / shares shares	Nov. 12, 2013 USD ($) bank shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) shares
Business Acquisition [Line Items]
Value of stock issued as a part of acquisition					$ 70,402	$ 34,981	$ 135,642
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	7,079,457
Value of stock issued as a part of acquisition					$ 346	$ 197	$ 885
Merger with Ameriana Bancorp
Business Acquisition [Line Items]
Percentage of interest acquired	100.00%				100.00%
Number of banking centers acquired | bank	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	$ 3,200				$ 3,200
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		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			10
Number of shares of common stock			4.0926
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
Merger with CFS Bancorp, Inc.
Business Acquisition [Line Items]
Percentage of interest acquired				100.00%
Number of banking centers acquired | bank				20
Stock issued as a part of acquisition (in shares) | shares				7,100,000
Value of stock issued as a part of acquisition				$ 135,600
Core deposit intangible				$ 7,313
Acquired intangible asset, expected useful life				10 years
Total purchase price				$ 135,642
Percentage of common stock received per shares owned through acquisition				0.65%
Pro forma nonrecurring expense							9,500
Pro forma revenue							$ 4,900