Acquisitions and Divestitures - Assets Acquired and Liabilities Assumed (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015	Apr. 17, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill	$ 244,000,000	$ 243,129,000		$ 202,724,000
Ameriana
Business Acquisition [Line Items]
Cash and cash equivalents		4,068,000
Interest-bearing time deposits		8,790,000
Investment securities		61,754,000
Loans		316,929,000
Premises and equipment		13,946,000
Federal Home Loan Bank stock		2,693,000
Other real estate owned		5,613,000
Interest receivable		1,306,000
Cash surrender value of life insurance		28,188,000
Other assets		6,713,000
Deposits		(383,718,000)
Interest payable		(24,000)
Federal Home Loan Bank Advances		(24,884,000)
Subordinated debentures		(5,487,000)
Other liabilities		(9,451,000)
Net tangible assets acquired		26,436,000
Core deposit intangible		5,342,000
Goodwill		38,624,000
Purchase price		$ 70,402,000
C Financial
Business Acquisition [Line Items]
Cash and cash equivalents			$ 2,496,000
Federal Funds sold			7,018,000
Interest-bearing time deposits			922,000
Loans			110,625,000
Premises and equipment			7,290,000
Federal Home Loan Bank stock			855,000
Interest receivable			292,000
Other assets			119,000
Deposits			(105,326,000)
Interest payable			(29,000)
Federal Home Loan Bank Advances			(18,958,000)
Other liabilities			(2,911,000)
Net tangible assets acquired			2,393,000
Core deposit intangible			981,000
Goodwill			11,126,000
Purchase price			$ 14,500,000