PARENT COMPANY STATEMENTS, Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities [Abstract]
Net income	$ 103,812	$ 91,230	$ 91,353
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Net change in other assets and other liabilities	(12,124)	(8,784)	(970)
Net cash provided by operating activities	131,261	116,463	122,104
Investing activities [Abstract]
Cash received for acquisitions, net of cash acquired of $0, $81,772, and $0, respectively	(575)	25,505	(924)
Net cash (used in) provided by investing activities	(121,998)	(274,161)	(331,132)
Financing activities [Abstract]
Issuance of common stock	10,543	9,774	9,417
Purchases of treasury stock	(3,470)	(9,126)	(4,368)
Sale of treasury stock	8,888	16,571	1,531
Net cash provided by (used in) financing activities	11,384	172,512	197,777
Change in cash and cash equivalents	20,647	14,814	(11,251)
Cash and cash equivalents at beginning of year	153,210	138,396	149,647
Cash and cash equivalents at end of year	173,857	153,210	138,396
Supplemental disclosures of cash flow information [Abstract]
Cash paid for interest	11,268	11,252	11,937
Supplemental disclosures of noncash financing activities [Abstract]
Dividends declared and unpaid	14,268	13,605	12,254
Common stock issued for acquisition	0	102,202	0
Cash acquired related to acquisition	0	81,772	0
Parent Company [Member]
Operating activities [Abstract]
Net income	103,812	91,230	91,353
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Equity in undistributed net income of subsidiaries	(15,483)	(18,264)	(32,098)
Net change in other assets and other liabilities	(215)	(27)	(479)
Net cash provided by operating activities	88,114	72,939	58,776
Investing activities [Abstract]
Proceeds from sale of investment securities	0	0	3
Cash received for acquisitions, net of cash acquired of $0, $81,772, and $0, respectively	0	25,505	0
Capital contributions to subsidiaries	0	(80,231)	0
Net cash (used in) provided by investing activities	0	(54,726)	3
Financing activities [Abstract]
Issuance of common stock	15,326	13,975	13,410
Purchases of treasury stock	(3,470)	(9,126)	(4,368)
Sale of treasury stock	8,888	16,571	1,531
Cash dividends paid	(55,048)	(49,273)	(46,178)
Net cash provided by (used in) financing activities	(34,304)	(27,853)	(35,605)
Change in cash and cash equivalents	53,810	(9,640)	23,174
Cash and cash equivalents at beginning of year	97,317	106,957	83,783
Cash and cash equivalents at end of year	151,127	97,317	106,957
Supplemental disclosures of cash flow information [Abstract]
Cash paid for interest	2,909	2,523	2,473
Supplemental disclosures of noncash financing activities [Abstract]
Dividends declared and unpaid	14,268	13,605	12,254
Capital contributions to subsidiaries	0	76,461	0
Common stock issued for acquisition	0	102,202	0
Cash acquired related to acquisition	$ 0	$ 81,772	$ 0