PARENT COMPANY FINANCIAL INFORMATION - CASH FLOWS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
OPERATING ACTIVITIES:
Net Income	$ 17,381	$ 20,303	$ 20,203	$ 16,251	$ 10,331	$ 14,511	$ 14,481	$ 14,989	$ 74,138	$ 54,312	$ 49,349
Adjustments to reconcile net income to net cash provided by operations:
Decrease (increase) in other assets									(2,166)	(3,909)	1,823
Increase (decrease) in other liabilities									1,358	(1,063)	3,520
Net cash provided by operating activities									122,402	91,730	86,725
INVESTING ACTIVITIES:
Net cash provided by (used in) investing activities									261,904	172,737	(384,404)
FINANCING ACTIVITIES:
Net proceeds from issuance of subordinated long-term debt									0	0	98,060
Purchase of common stock									(47,193)	0	(10,199)
Proceeds from issuance of common stock									0	0	75,992
Cash dividends paid									(41,979)	(32,199)	(25,963)
Net cash (used in) provided by financing activities									(462,279)	(235,429)	386,358
Net increase (decrease) in cash and cash equivalents									(77,973)	29,038	88,679
Cash and cash equivalents at beginning of period				198,692				169,654	198,692	169,654	80,975
Cash and cash equivalents at end of period	120,719				198,692				120,719	198,692	169,654
Parent
OPERATING ACTIVITIES:
Net Income									74,138	54,312	49,349
Adjustments to reconcile net income to net cash provided by operations:
Amortization									164	153	45
Equity in undistributed earnings of subsidiaries									6,498	(36,525)	(23,581)
Decrease (increase) in other assets									6,060	(2,113)	(1,035)
Increase (decrease) in other liabilities									1,377	(155)	1,564
Net cash provided by operating activities									88,237	15,672	26,342
INVESTING ACTIVITIES:
Investment in subsidiaries									0	890	(126,000)
Net cash paid in acquisition									0	(22,801)	0
Net cash provided by (used in) investing activities									0	(21,911)	(126,000)
FINANCING ACTIVITIES:
Net proceeds from issuance of subordinated long-term debt									0	0	98,060
Purchase of common stock									(47,193)	0	(10,199)
Proceeds from issuance of common stock									3,883	3,953	78,962
Cash dividends paid									(41,979)	(32,199)	(25,963)
Net cash (used in) provided by financing activities									(85,289)	(28,246)	140,860
Net increase (decrease) in cash and cash equivalents									2,948	(34,485)	41,202
Cash and cash equivalents at beginning of period				$ 8,483				$ 42,968	8,483	42,968	1,766
Cash and cash equivalents at end of period	$ 11,431				$ 8,483				$ 11,431	$ 8,483	$ 42,968