Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net income	$ 31,913,000	$ 27,020,000	$ 17,331,000
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	9,576,000	11,654,000	7,613,000
Accretion of acquired loans	(4,925,000)	(5,338,000)	(3,194,000)
Provision for loan losses	2,900,000	(1,000,000)	(3,000,000)
Deferred income tax expense	(812,000)	4,412,000	4,506,000
Stock-based compensation expense	1,459,000	684,000	714,000
Stock grants to directors for retainer fee	327,000	403,000	155,000
Proceeds from sales of mortgage loans held for sale	114,757,000	120,880,000	67,422,000
Origination of mortgage loans held for sale	(110,778,000)	(116,997,000)	(65,392,000)
Net gain on sales of mortgage loans held for sale	(3,699,000)	(3,626,000)	(1,625,000)
Gain on trust preferred securities repurchase	(2,970,000)	0	0
Net gain from sales and valuation write-downs of foreclosed assets	(520,000)	(62,000)	(894,000)
Net loss from sales and valuation write-downs of former bank premises	35,000	0	0
Net loss from sales of premises and equipment	174,000	55,000	25,000
Net (gain) loss from sales of available for sale securities	1,000	(17,000)	0
Earnings on bank owned life insurance	(1,264,000)	(1,113,000)	(1,184,000)
Net change in:
Accrued interest receivable	122,000	(321,000)	(11,000)
Other assets	(648,000)	(4,815,000)	1,795,000
Accrued interest and other liabilities	(1,046,000)	4,185,000	(9,822,000)
Net cash from operating activities	34,602,000	36,004,000	14,439,000
Cash flows from investing activities
Cash received in merger	0	0	91,806,000
Purchases of securities available for sale	(164,336,000)	(10,645,000)	(19,874,000)
Proceeds from maturities, calls and repayments of securities available for sale	172,173,000	93,873,000	75,880,000
Proceeds from sales of securities available for sale	264,000	1,483,000	0
Purchases of Federal Home Loan Bank stock	(459,000)	0	0
Proceeds from Federal Home Loan Bank stock redemption	0	6,132,000	5,527,000
Loan originations and payments, net	(97,282,000)	(188,932,000)	(90,853,000)
Purchases of bank owned life insurance	(7,000,000)	0	0
Purchases of premises and equipment, net	(2,025,000)	(1,081,000)	(2,175,000)
Proceeds from sales of former bank premises	45,000	0	0
Proceeds from sales of foreclosed assets	2,059,000	2,967,000	4,427,000
Net cash from (for) investing activities	(96,561,000)	(96,203,000)	64,738,000
Cash flows from financing activities
Net decrease in time deposits	(20,854,000)	(147,106,000)	(58,927,000)
Net increase (decrease) in all other deposits	120,457,000	146,944,000	(11,307,000)
Net increase (decrease) in securities sold under agreements to repurchase	(23,061,000)	(12,798,000)	43,780,000
Proceeds from Federal Home Loan Bank advances	110,000,000	20,000,000	0
Maturities of Federal Home Loan Bank advances	(3,000,000)	(6,000,000)	(3,000,000)
Proceeds from stock option exercises, net of cashless exercises	978,000	891,000	282,000
Employee stock purchase plan	36,000	44,000	23,000
Dividend reinvestment plan	1,601,000	655,000	209,000
Repurchase of common stock	(3,732,000)	(15,762,000)	0
Repurchase of trust preferred securities	(8,030,000)	0	0
Payment of cash dividends to common shareholders	(18,731,000)	(9,516,000)	(24,464,000)
Net cash from (for) financing activities	155,664,000	(22,648,000)	(53,404,000)
Net change in cash and cash equivalents	93,705,000	(82,847,000)	25,773,000
Cash and cash equivalents at beginning of period	89,891,000	172,738,000	146,965,000
Cash and cash equivalents at end of period	183,596,000	89,891,000	172,738,000
Supplemental disclosures of cash flows information
Interest	12,477,000	11,618,000	11,439,000
Federal income taxes	15,125,000	8,000,000	2,625,000
Noncash financing and investing activities:
Transfers from loans to foreclosed assets	414,000	2,203,000	1,490,000
Transfers from bank premises to other real estate owned	381,000	0	0
Common stock issued in connection with the Firstbank merger	$ 0	$ 0	$ 173,310,000