PARENT COMPANY FINANCIAL INFORMATION - Statements of Condition (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 297,003	$ 146,103
Investments available-for-sale (at fair value)	1,348,021	1,073,333
Equity securities	65,760	51,803
Goodwill	370,223	347,149	$ 347,149
Other assets	265,859	216,593
Total assets	12,798,429	8,629,002	8,243,272
Liabilities
Subordinated debt	227,088	209,406
Accrued expenses and other liabilities	146,085	118,921
Total liabilities	11,328,474	7,496,028
Stockholders’ Equity:
Common stock	47,057	34,970
Additional paid-in capital	846,922	586,622
Retained earnings	557,271	515,714
Accumulated other comprehensive income/ (loss)	18,705	(4,332)
Total stockholders' equity	1,469,955	1,132,974	$ 1,067,903	$ 563,816
Total liabilities and stockholders' equity	12,798,429	8,629,002
Parent Company
Assets
Cash and cash equivalents	63,943	90,361
Investments available-for-sale (at fair value)	9,925	10,430
Equity securities	568	0
Investment in subsidiary	1,589,483	1,242,229
Goodwill	1,292	1,292
Other assets	2,684	1,480
Total assets	1,667,895	1,345,792
Liabilities
Subordinated debt	196,454	209,406
Accrued expenses and other liabilities	1,486	3,412
Total liabilities	197,940	212,818
Stockholders’ Equity:
Common stock	47,057	34,970
Additional paid-in capital	846,922	586,622
Retained earnings	557,271	515,714
Accumulated other comprehensive income/ (loss)	18,705	(4,332)
Total stockholders' equity	1,469,955	1,132,974
Total liabilities and stockholders' equity	$ 1,667,895	$ 1,345,792