Consolidated Statements of Changes in Shareholders' Equity - USD ($)	Preferred Stock [Member]	Common Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Beginning Balances at Dec. 31, 2013	$ 0	$ 162,999,000	$ (4,101,000)	$ (5,573,000)	$ 153,325,000
Common stock issued in connection with Firstbank merger (8,087,272 shares)		173,310,000			173,310,000
Issuance of stock options to replace existing Firstbank options at merger date		1,664,000			1,664,000
Employee stock purchase plan		23,000			23,000
Dividend reinvestment plan		209,000			209,000
Stock option exercises		282,000			282,000
Stock grants to directors for retainer fees		155,000			155,000
Stock-based compensation expense		714,000			714,000
Cash dividends		(21,452,000)	(3,012,000)		(24,464,000)
Net income			17,331,000		17,331,000
Change in net unrealized gain on securities available for sale, net of tax effect				5,582,000	5,582,000
Change in fair value of interest rate swap, net of tax effect				7,000	7,000
Balances at Dec. 31, 2014	0	317,904,000	10,218,000	16,000	328,138,000
Employee stock purchase plan		44,000			44,000
Dividend reinvestment plan		655,000			655,000
Stock option exercises		891,000			891,000
Stock grants to directors for retainer fees		403,000			403,000
Stock-based compensation expense		684,000			684,000
Cash dividends			(9,516,000)		(9,516,000)
Net income			27,020,000		27,020,000
Change in net unrealized gain on securities available for sale, net of tax effect				1,247,000	1,247,000
Change in fair value of interest rate swap, net of tax effect				0	0
Balances at Dec. 31, 2015	0	304,819,000	27,722,000	1,263,000	333,804,000
Share repurchase program		(15,762,000)			(15,762,000)
Employee stock purchase plan		36,000			36,000
Dividend reinvestment plan		1,601,000			1,601,000
Stock option exercises		978,000			978,000
Stock grants to directors for retainer fees		327,000			327,000
Stock-based compensation expense		1,459,000			1,459,000
Cash dividends			(18,731,000)		(18,731,000)
Net income			31,913,000		31,913,000
Change in net unrealized gain on securities available for sale, net of tax effect				(6,954,000)	(6,954,000)
Change in fair value of interest rate swap, net of tax effect				110,000	110,000
Balances at Dec. 31, 2016	$ 0	305,488,000	$ 40,904,000	$ (5,581,000)	340,811,000
Share repurchase program		$ (3,732,000)			$ (3,732,000)