PARENT COMPANY FINANCIAL INFORMATION (Statements of Condition) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 146,103	$ 101,481
Investments available-for-sale (at fair value)	1,073,333	937,335
Investments held-to-maturity	0	0
Goodwill	347,149	347,149	$ 85,768
Other assets	216,593	145,074
Total assets	8,629,002	8,243,272	5,446,675
Liabilities
Subordinated debentures	209,406	37,425
Accrued expenses and other liabilities	118,921	47,024
Total liabilities	7,496,028	7,175,369
Stockholders Equity
Common stock	34,970	35,531
Additional paid in capital	586,622	606,573
Retained earnings	515,714	441,553
Accumulated other comprehensive income (loss)	(4,332)	(15,754)	(6,857)	$ (6,614)
Total stockholders equity	1,132,974	1,067,903	$ 563,816	$ 533,572
Total liabilities and stockholders equity	8,629,002	8,243,272
Parent Company [Member]
Assets
Cash and cash equivalents	90,361	23,334
Investments available-for-sale (at fair value)	10,430	10,118
Investment in subsidiary	1,242,229	1,066,550
Goodwill	1,292	1,292
Other assets	1,480	4,463
Total assets	1,345,792	1,105,757
Liabilities
Subordinated debentures	209,406	37,425
Accrued expenses and other liabilities	3,412	429
Total liabilities	212,818	37,854
Stockholders Equity
Common stock	34,970	35,531
Additional paid in capital	586,622	606,573
Retained earnings	515,714	441,553
Accumulated other comprehensive income (loss)	(4,332)	(15,754)
Total stockholders equity	1,132,974	1,067,903
Total liabilities and stockholders equity	$ 1,345,792	$ 1,105,757