PARENT COMPANY FINANCIAL INFORMATION (Statements of Cash Flows) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows from Operating Activities:
Net income	$ 28,457	$ 29,383	$ 28,276	$ 30,317	$ 25,566	$ 29,234	$ 24,399	$ 21,665	$ 116,433	$ 100,864	$ 53,209
Adjustments to reconcile net income to net cash provided by operating activities:
Share based compensation expense									3,042	2,645	2,164
Net change in other liabilities									(5,804)	(2,721)	(1,007)
Other-net									(721)	3,970	5,174
Net cash provided by operating activities									99,943	147,646	69,417
Cash Flows from Investing Activities:
Purchase of investment available-for-sale									(326,604)	(161,349)	(125,028)
Acquistion of business activity, net of cash acquired									0	32,487	0
Net cash used in investing activities									(241,276)	(505,004)	(392,347)
Cash Flows from Financing Activities:
Retirement of subordinated debt									0	0	(30,000)
Redemption of stock warrant									(24,284)	0	0
Proceeds from issuance of common stock									1,433	1,395	1,200
Stock tendered for payment of withholding taxes									(703)	(760)	(952)
Repurchase of common stock									(24,284)	0	0
Dividends paid									(42,272)	(39,277)	(25,134)
Net cash provided by financing activities									185,955	346,339	301,305
Net increase (decrease) in cash and cash equivalents									44,622	(11,019)	(21,625)
Cash and cash equivalents at beginning of period				101,481				112,500	101,481	112,500	134,125
Cash and cash equivalents at end of period	146,103				101,481				146,103	101,481	112,500
Parent Company [Member]
Cash Flows from Operating Activities:
Net income									116,433	100,864	53,209
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed income-subsidiary									(76,629)	(63,371)	(27,270)
Decrease in receivable from subsidiary bank									0	0	30,000
Share based compensation expense									3,042	2,645	2,164
Tax benefit from stock options exercised									7	8	0
Other-net									0	(3,252)	(4,028)
Net cash provided by operating activities									42,853	36,894	54,075
Cash Flows from Investing Activities:
Purchase of investment available-for-sale									0	0	3,179
Investment in subsidiary									(85,000)	0	0
Acquistion of business activity, net of cash acquired									0	11,845	0
Net cash used in investing activities									(85,000)	11,845	3,179
Cash Flows from Financing Activities:
Retirement of subordinated debt									0	0	(30,000)
Proceeds from issuance of subordinated debt									175,000	0	0
Proceeds from issuance of common stock									1,433	1,395	1,200
Stock tendered for payment of withholding taxes									(703)	(760)	(952)
Repurchase of common stock									(24,284)	0	0
Dividends paid									(42,272)	(39,277)	(25,134)
Net cash provided by financing activities									109,174	(38,642)	(54,886)
Net increase (decrease) in cash and cash equivalents									67,027	10,097	2,368
Cash and cash equivalents at beginning of period				$ 23,334				$ 13,237	23,334	13,237	10,869
Cash and cash equivalents at end of period	$ 90,361				$ 23,334				$ 90,361	$ 23,334	$ 13,237