FAIR VALUE DISCLOSURES OF FINANCIAL ASSETS AND LIABILITIES - Book Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Financial assets:
Investment securities available-for-sale	$ 3,954,918	$ 4,093,060
Stock in FHLB of Pittsburgh	9,399	24,116
Accrued interest receivable	77,830	74,448
Financial liabilities:
Deposits	16,427,956	16,203,569
Accrued interest payable	25,718	5,174
Book Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	1,115,560	837,258
Book Value | Level 2
Financial assets:
Investment securities available-for-sale	3,954,918	4,093,060
Investment securities held-to-maturity, net	1,079,768	1,111,619
Loans, held for sale	43,065	42,985
Stock in FHLB of Pittsburgh	9,399	24,116
Accrued interest receivable	77,830	74,448
Financial liabilities:
Deposits	16,427,956	16,203,569
Borrowed funds	899,493	726,894
Accrued interest payable	25,718	5,174
Book Value | Level 3
Financial assets:
Other investments	24,560	26,120
Loans and leases, net	12,168,047	11,759,992
Financial liabilities:
Standby letters of credit	674	739
Book Value | Levels 2, 3
Financial assets:
Other assets	151,942	156,993
Financial liabilities:
Other liabilities	163,855	173,622
Fair Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	1,115,560	837,258
Fair Value | Level 2
Financial assets:
Investment securities available-for-sale	3,954,918	4,093,060
Investment securities held-to-maturity, net	1,005,843	1,040,104
Loans, held for sale	43,065	42,985
Stock in FHLB of Pittsburgh	9,399	24,116
Accrued interest receivable	77,830	74,448
Financial liabilities:
Deposits	16,386,841	16,156,124
Borrowed funds	883,174	709,014
Accrued interest payable	25,718	5,174
Fair Value | Level 3
Financial assets:
Other investments	24,560	26,120
Loans and leases, net	12,204,153	11,567,888
Financial liabilities:
Standby letters of credit	674	739
Fair Value | Levels 2, 3
Financial assets:
Other assets	151,942	156,993
Financial liabilities:
Other liabilities	$ 163,855	$ 173,622