CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net income	$ 53,209	$ 48,250	$ 45,355
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,976	7,958	7,305
Provision for loan losses	2,977	5,546	5,371
Share based compensation expense	2,164	2,139	1,979
Deferred income tax expense	6,089	349	(3)
Origination of loans held for sale	(142,877)	(196,726)	(193,316)
Proceeds from sales of loans held for sale	149,367	239,705	191,232
Gains on sales of loans held for sale	(3,403)	(3,877)	(2,861)
(Gains) losses on sales of other real estate owned	(68)	48	267
Investment securities gains	(1,273)	(1,932)	(36)
Tax benefits associated with share based compensation	1,809	125	350
Increase (Decrease) in Operating Capital [Abstract]
Net (increase) decrease in accrued interest receivable	(891)	(1,146)	(809)
Net decrease in other assets	(9,829)	(5,134)	(2,015)
Net increase (decrease) in accrued expenses and other liabilities	(1,007)	(2,932)	(6,267)
Other - net	5,174	(1,873)	4,628
Net cash provided by operating activities	69,417	90,500	51,180
Investing activities:
Purchases of other equity securities		(4,758)
Proceeds of other equity securities	576		101
Purchases of investments held-to-maturity	0	0	(2,100)
Purchases of investments available-for-sale	(125,028)	(287,211)	(46,190)
Proceeds from sales of investment available-for-sale	2,251	40,863	0
Proceeds from maturities, calls and principal payments of investments held-to-maturity	0	5,004	12,943
Proceeds from maturities, calls and principal payments of investments available-for-sale	123,762	298,803	121,994
Net increase in loans	(427,773)	(469,942)	(372,203)
Proceeds from the sales of other real estate owned	1,275	1,393	2,112
Proceeds from sales of loans held for investment	40,031	0	0
Acquisition of business activity, net of cash acquired	0	(1,347)	0
Expenditures for premises and equipment	(7,441)	(5,798)	(8,572)
Net cash (used) in investing activities	(392,347)	(422,993)	(291,915)
Financing activities:
Net increase in deposits	386,118	313,814	197,221
Net increase/(decrease) in retail repurchase agreements and federal funds purchased	(5,760)	15,974	34,713
Proceeds from advances from FHLB	3,965,000	2,665,000	2,274,000
Repayment of advances from FHLB	(3,989,167)	(2,560,000)	(2,244,000)
Retirement of subordinated debt	(30,000)	(5,000)	0
Proceeds from issuance of common stock	1,200	1,580	1,174
Stock tendered for payment of withholding taxes	(952)	(683)	(687)
Repurchase of common stock	0	(13,273)	(22,624)
Dividends paid	(25,134)	(23,676)	(22,397)
Net cash provided by financing activities	301,305	393,736	217,400
Net increase (decrease) in cash and cash equivalents	(21,625)	61,243	(23,335)
Cash and cash equivalents at beginning of period	134,125	72,882	96,217
Cash and cash equivalents at end of period	112,500	134,125	72,882
Supplemental Disclosures:
Interest payments	26,377	21,377	20,040
Income tax payments	31,738	22,331	21,060
Transfer of Investments Held-to-maturity to Available For Sale Securities	0	203,118	0
Transfer from loans to residential mortgage loans held for sale	39,744	36,867	0
Transfers from loans to other real estate owned	$ 1,588	$ 637	$ 1,947