PARENT COMPANY STATEMENTS, Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands			12 Months Ended
	Sep. 18, 2019	Jul. 12, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities [Abstract]
Net income			$ 169,063	$ 168,641	$ 150,717
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Net change in other assets and other liabilities			2,545	10,252	26,090
Net cash provided by operating activities			202,502	221,408	189,674
Investing activities [Abstract]
Cash paid for acquisitions, net of cash acquired of $1,328, $0, and $150,534, respectively	$ (500)	$ (95,034)	(4,653)	(1,737)	(107,414)
Net cash (used in)/provided by investing activities			(157,054)	17,495	131,371
Financing activities [Abstract]
Issuance of common stock			6,915	6,443	4,563
Purchase of treasury stock			(286)	(298)	(3,306)
Sale of treasury stock			6,884	12,561	10,060
Increase in deferred compensation arrangements			286	298	3,306
Net cash used in financing activities			(52,252)	(248,107)	(273,864)
Change in cash and cash equivalents			(6,804)	(9,204)	47,181
Cash and cash equivalents at beginning of year			211,834	221,038	173,857
Cash and cash equivalents at end of year			205,030	211,834	221,038
Supplemental disclosures of cash flow information [Abstract]
Cash paid for interest			25,425	17,926	13,705
Supplemental disclosures of noncash financing activities [Abstract]
Dividends declared and unpaid			21,342	19,808	17,460
Common stock issued for acquisition			0	0	343,132
Cash acquired from acquisition			90,381	16	52,132
Parent Company [Member]
Operating activities [Abstract]
Net income			169,063	168,641	150,717
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Equity in undistributed net income of subsidiaries			(27,753)	(65,026)	(26,175)
Net change in other assets and other liabilities			86	(1,084)	1,870
Net cash provided by operating activities			141,396	102,531	126,412
Investing activities [Abstract]
Proceeds from redemption of investment securities			0	776	0
Cash paid for acquisitions, net of cash acquired of $1,328, $0, and $150,534, respectively			(92,056)	0	(139,471)
Return of capital from/(capital contributions to)			100,680	0	(11,063)
Net cash (used in)/provided by investing activities			8,624	776	(150,534)
Financing activities [Abstract]
Repayment of advances from subsidiaries			(1,652)	0	0
Repayment of borrowings			(22,681)	(25,207)	0
Issuance of common stock			12,200	12,507	9,700
Purchase of treasury stock			(286)	(298)	(3,306)
Sale of treasury stock			6,884	12,561	10,060
Increase in deferred compensation arrangements			286	298	3,306
Cash dividends paid			(80,241)	(71,495)	(62,305)
Net cash used in financing activities			(85,490)	(71,634)	(42,545)
Change in cash and cash equivalents			64,530	31,673	(66,667)
Cash and cash equivalents at beginning of year			116,133	84,460	151,127
Cash and cash equivalents at end of year			180,663	116,133	84,460
Supplemental disclosures of cash flow information [Abstract]
Cash paid for interest			4,306	4,857	3,826
Supplemental disclosures of noncash financing activities [Abstract]
Dividends declared and unpaid			21,342	19,808	17,460
Advances from subsidiaries			1,691	0	0
Capital contributions to subsidiaries			0	0	513,769
Common stock issued for acquisition			0	0	343,132
Cash acquired from acquisition			$ 1,328	$ 0	$ 150,534