PARENT COMPANY FINANCIAL INFORMATION - CASH FLOWS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES:
Net Income	$ 29,572	$ 27,074	$ 21,554	$ 3,953	$ 17,335	$ 19,792	$ 18,610	$ 18,817	$ 82,153	$ 74,554	$ 74,138
Adjustments to reconcile net income to net cash provided by operations:
Stock compensation expense									3,020	2,388	2,317
Net change in other assets									(6,445)	(12,275)	(2,166)
Net change in other liabilities									(15,594)	(13,377)	1,358
Net cash provided by operating activities									90,520	80,606	122,402
INVESTING ACTIVITIES:
Net cash (used in) provided by investing activities									(223,735)	(566,830)	261,904
FINANCING ACTIVITIES:
Net proceeds from issuance of subordinated long-term debt									98,478	0	0
Purchase of common stock									(30,989)	(2,181)	(47,193)
Cash dividends paid									(43,204)	(42,521)	(41,979)
Net cash provided by (used in) financing activities									130,926	476,202	(462,279)
Cash and cash equivalents at beginning of period				110,697					110,697
Cash and cash equivalents at end of period	108,408				110,697				108,408	110,697
Parent
OPERATING ACTIVITIES:
Net Income									82,153	74,554	74,138
Adjustments to reconcile net income to net cash provided by operations:
Amortization									202	173	164
Stock compensation expense									197	0	0
Equity in undistributed earnings of subsidiaries									(19,092)	(33,466)	6,498
Net change in other assets									(546)	104	6,060
Net change in other liabilities									(58)	(979)	1,377
Net cash provided by operating activities									62,856	40,386	88,237
INVESTING ACTIVITIES:
Net cash (used in) provided by investing activities									0	0	0
FINANCING ACTIVITIES:
Net proceeds from issuance of subordinated long-term debt									98,478	0	0
Purchase of common stock									(30,989)	(2,181)	(47,193)
Proceeds from issuance of common stock									2,723	3,037	3,883
Cash dividends paid									(43,204)	(42,521)	(41,979)
Net cash provided by (used in) financing activities									27,008	(41,665)	(85,289)
Net increase (decrease) in cash and cash equivalents									89,864	(1,279)	2,948
Cash and cash equivalents at beginning of period				$ 10,152				$ 11,431	10,152	11,431	8,483
Cash and cash equivalents at end of period	$ 100,016				$ 10,152				$ 100,016	$ 10,152	$ 11,431