Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Income	$ 33,015,000	$ 23,852,000	$ 91,688,000	$ 65,140,000
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization			12,088,000	11,497,000
Provision for loan losses	1,075,000	0	3,575,000	1,650,000
Deferred income tax expense			176,000	443,000
Net unrealized (gain) loss on equity securities			113,000
Net gain on sale of securities			(6,000)	(13,000)
Net (gain) loss on bank premises and equipment			8,000	(93,000)
Net loss on other real estate owned and foreclosed assets			1,000	308,000
Realized gain on sale leaseback transaction			(585,000)	(775,000)
Stock based compensation			3,161,000	2,346,000
Increase in cash surrender value of life insurance policies			(2,929,000)	(3,000,000)
Gain Realized on Life Insurance Policies	(1,463,000)	0	(1,463,000)	0
Change in Fair Value on Loans Held for Sale	(103,000)	108,000	(147,000)	102,000
Net change in:
Trading assets			(257,000)	(494,000)
Loans held for sale			(5,516,000)	578,000
Other assets			(12,179,000)	4,561,000
Increase (Decrease) in Other Operating Liabilities			16,066,000	6,177,000
Total adjustments			12,106,000	23,287,000
Net cash provided by operating activities			103,794,000	88,427,000
Cash flows used in investing activities
Proceeds from Sale of Debt and Equity Securities, FV-NI, Held-for-investment			30,000
Proceeds from Sale of Available-for-sale Securities, Equity				0
Increase (Decrease) in Equity Securities, FV-NI			(305,000)	0
Proceeds from Sale of Debt Securities, Available-for-sale				523,000
Proceeds from maturities and principal repayments of securities available for sale			41,964,000	40,228,000
Payments to Acquire Debt Securities, Available-for-sale			(63,844,000)	(104,284,000)
Proceeds from maturities and principal repayments of securities held to maturity			62,650,000	58,308,000
Purchases of securities held to maturity			(118,256,000)	(49,802,000)
Net redemption (purchases) of Federal Home Loan Bank stock			(1,510,000)	386,000
Investments in low income housing projects			(2,598,000)	(4,713,000)
Purchases of life insurance policies			(116,000)	(115,000)
Proceeds from Life Insurance Policy			2,850,000		$ 0
Net increase in loans			(173,224,000)	(138,622,000)
Cash Acquired in Excess of Payments to Acquire Business			0	6,289,000
Purchases of bank premises and equipment			(8,123,000)	(18,643,000)
Proceeds from the sale of bank premises and equipment			96,000	1,919,000
Proceeds from the sale of other real estate owned and foreclosed assets			308,000	1,531,000
Net cash used in investing activities			(260,078,000)	(206,995,000)
Cash flows provided by financing activities
Net increase (decrease) in time deposits			19,226,000	(35,947,000)
Net increase in other deposits			227,836,000	147,331,000
Increase (Decrease) in Federal Home Loan Bank Advances Long Term			(2,475,000)	0
Net increase (decrease) in customer repurchase agreements			(21,503,000)	2,757,000
Proceeds from exercise of stock options, net of cash paid			(184,000)
Payments for Repurchase of Common Stock				(5,000)
Restricted stock awards issued, net of awards surrendered			(1,344,000)	(1,363,000)
Proceeds from shares issued under direct stock purchase plan			1,792,000	1,230,000
Common dividends paid			(29,701,000)	(25,265,000)
Net cash provided by financing activities			194,015,000	88,738,000
Net increase (decrease) in cash and cash equivalents			37,731,000	(29,830,000)
Cash and cash equivalents at beginning of year			213,116,000	289,095,000	289,095,000
Cash and cash equivalents at end of period	250,847,000	259,265,000	250,847,000	259,265,000	$ 213,116,000
Supplemental schedule of noncash investing and financing activities
Real Estate Owned, Transfer from Real Estate Owned				564,000
Net increase in capital commitments relating to low income housing project investments			65,000	248,000
Stock Issued During Period, Value, Acquisitions			0	23,468,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	0	179,252,000	0	179,252,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	$ 0	$ 162,073,000	$ 0	$ 162,073,000