PARENT COMPANY STATEMENTS, Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities [Abstract]
Net income	$ 91,230	$ 91,353	$ 78,829
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
Net change in other assets and other liabilities	8,784	(127)	11,762
Net cash provided by operating activities	116,463	123,201	103,184
Investing activities [Abstract]
Cash received for acquisitions, net of cash acquired of $81,772, $0, and $0, respectively	25,505	(924)	291,980
Net cash (used in)/provided by investing activities	(274,161)	(332,229)	553,258
Financing activities [Abstract]
Issuance of common stock	9,774	9,417	15,239
Purchase of treasury stock	(9,126)	(4,368)	0
Sale of treasury stock	16,571	1,531	0
Net cash provided by/(used in) financing activities	172,512	197,777	(735,353)
Change in cash and cash equivalents	14,814	(11,251)	(78,911)
Cash and cash equivalents at beginning of year	138,396	149,647	228,558
Cash and cash equivalents at end of year	153,210	138,396	149,647
Supplemental disclosures of cash flow information [Abstract]
Cash paid for interest	11,252	11,937	30,141
Supplemental disclosures of noncash financing activities [Abstract]
Dividends declared and unpaid	13,605	12,254	11,332
Common stock issued for acquisition	102,201	0	0
Cash acquired related to acquisition	81,772	0	0
Parent Company [Member]
Operating activities [Abstract]
Net income	91,230	91,353	78,829
Adjustments to reconcile net income to net cash provided by operating activities [Abstract]
(Gain)/loss on sale of investments	0	0	(9)
Equity in undistributed net income of subsidiaries	(18,264)	(32,098)	(14,448)
Net change in other assets and other liabilities	(27)	(479)	(221)
Net cash provided by operating activities	72,939	58,776	64,151
Investing activities [Abstract]
Proceeds from sale of investment securities	0	3	114
Cash received for acquisitions, net of cash acquired of $81,772, $0, and $0, respectively	25,505	0	0
Capital contributions to subsidiaries	(80,231)	0	0
Net cash (used in)/provided by investing activities	(54,726)	3	114
Financing activities [Abstract]
Issuance of common stock	13,975	13,410	19,200
Purchase of treasury stock	(9,126)	(4,368)	0
Sale of treasury stock	16,571	1,531	0
Cash dividends paid	(49,273)	(46,178)	(43,482)
Net cash provided by/(used in) financing activities	(27,853)	(35,605)	(24,282)
Change in cash and cash equivalents	(9,640)	23,174	39,983
Cash and cash equivalents at beginning of year	106,957	83,783	43,800
Cash and cash equivalents at end of year	97,317	106,957	83,783
Supplemental disclosures of cash flow information [Abstract]
Cash paid for interest	2,523	2,473	2,521
Supplemental disclosures of noncash financing activities [Abstract]
Dividends declared and unpaid	13,605	12,254	11,332
Capital contributions to subsidiaries	76,461	0	0
Common stock issued for acquisition	102,202	0	0
Cash acquired related to acquisition	$ 81,772	$ 0	$ 0