Consolidated Statement of Shareholders' Equity - USD ($)	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Midwest Bancshares, Inc.	Midwest Bancshares, Inc. Common Stock	Ohio Heritage Bancorp, Inc.	Ohio Heritage Bancorp, Inc. Common Stock	North Akron Savings Bank	North Akron Savings Bank Common Stock	NB&T Financial Group, Inc. [Member] Common Stock
Balance at beginning of period at Dec. 31, 2012	$ 221,728,000	$ 167,039,000	$ 69,158,000	$ 654,000	$ (15,123,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,574,000		17,574,000
Other comprehensive income, net of tax	(13,898,000)			(13,898,000)
Cash dividends declared	(5,834,000)		(5,834,000)
Tax benefit from exercise of stock options	79,000	79,000
Reissuance of treasury stock for deferred compensation plan for Boards of Directors	(168,000)				(168,000)
Purchase of treasury stock	228,000				228,000
Common shares issued under dividend reinvestment plan	423,000	423,000
Common shares issued under compensation plan for Board of Directors	(179,000)	34,000			(213,000)
Stock-based compensation expense	1,362,000	1,362,000
Balance at end of period at Dec. 31, 2013	221,553,000	168,869,000	80,898,000	(13,244,000)	(14,970,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,684,000		16,684,000
Other comprehensive income, net of tax	11,943,000			11,943,000
Cash dividends declared	(7,191,000)		(7,191,000)
Stock Issued During Period, Value, Stock Options Exercised	72,000				72,000
Tax benefit from exercise of stock options	85,000	85,000
Reissuance of treasury stock for deferred compensation plan for Boards of Directors	(175,000)				(175,000)
Reissuance of treasury stock for common stock awards	0	(10,000)			10,000
Purchase of treasury stock	520,000				520,000
Common shares issued under dividend reinvestment plan	409,000	409,000
Common shares issued under compensation plan for Board of Directors	207,000	(14,000)			221,000
Stock-based compensation expense	2,111,000	1,813,000			298,000
Stock Issued During Period, Value, Acquisitions						$ 6,305,000	$ 6,305,000	$ 32,017,000	$ 32,017,000	$ 16,106,000	$ 16,106,000
Proceeds from Issuance of Private Placement	40,162,000	40,162,000
Balance at end of period at Dec. 31, 2014	340,118,000	265,742,000	90,391,000	(1,301,000)	(14,714,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	10,941,000		10,941,000
Other comprehensive income, net of tax	942,000			942,000
Cash dividends declared	(10,542,000)		(10,542,000)
Tax benefit from exercise of stock options	51,000	51,000
Reissuance of treasury stock for deferred compensation plan for Boards of Directors	(184,000)				(184,000)
Purchase of treasury stock	741,000				741,000
Common shares issued under dividend reinvestment plan	397,000	397,000
Common shares issued under compensation plan for Board of Directors	134,000	(43,000)			177,000
Stock-based compensation expense	1,843,000	1,843,000
Common shares issued under employee stock purchase plan	(435,000)	(69,000)			(504,000)
Stock Issued During Period, Value, Acquisitions											$ 76,027,000	$ 76,027,000
Balance at end of period at Dec. 31, 2015	$ 419,789,000	$ 343,948,000	$ 90,790,000	$ (359,000)	$ (14,590,000)