FAIR VALUE DISCLOSURES OF FINANCIAL ASSETS AND LIABILITIES - Book Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Financial assets:
Investment securities available-for-sale	$ 4,496,087	$ 5,205,311
Stock in FHLB of Pittsburgh	10,118	6,073
Accrued interest receivable	55,718	41,596
Financial liabilities:
Deposits	17,269,607	13,240,062
Accrued interest payable	3,091	736
Book Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	1,676,609	1,532,939
Book Value | Levels 2, 3
Financial liabilities:
Other liabilities	118,139	23,291
Book Value | Level 2
Financial assets:
Investment securities available-for-sale	4,496,087	5,205,311
Investment securities held-to-maturity, net	1,064,182	90,642
Loans, held for sale	60,775	113,349
Stock in FHLB of Pittsburgh	10,118	6,073
Accrued interest receivable	55,718	41,596
Other assets	102,196	5,153
Financial liabilities:
Deposits	17,269,607	13,240,062
Borrowed funds	369,783	239,477
Accrued interest payable	3,091	736
Book Value | Level 3
Financial assets:
Other investments	21,064	10,518
Loans and leases, net	11,340,711	7,791,482
Financial liabilities:
Standby letters of credit	504	674
Fair Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	1,676,609	1,532,939
Fair Value | Levels 2, 3
Financial liabilities:
Other liabilities	118,139	23,291
Fair Value | Level 2
Financial assets:
Investment securities available-for-sale	4,496,087	5,205,311
Investment securities held-to-maturity, net	1,063,352	94,131
Loans, held for sale	60,775	113,349
Stock in FHLB of Pittsburgh	10,118	6,073
Accrued interest receivable	55,718	41,596
Other assets	102,196	5,153
Financial liabilities:
Deposits	17,237,428	13,236,816
Borrowed funds	345,942	225,119
Accrued interest payable	3,091	736
Fair Value | Level 3
Financial assets:
Other investments	21,064	10,518
Loans and leases, net	11,115,598	7,723,867
Financial liabilities:
Standby letters of credit	$ 504	$ 674