FAIR VALUE DISCLOSURES OF FINANCIAL ASSETS AND LIABILITIES - Schedule of Book Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Financial assets:
Investment securities available-for-sale	$ 3,691,541	$ 4,093,060
Stock in FHLB of Pittsburgh	12,199	24,116
Accrued interest receivable	81,909	74,448
Financial liabilities:
Deposits	15,986,369	16,203,569
Accrued interest payable	42,481	5,174
Book Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	611,480	837,258
Book Value | Level 2
Financial assets:
Investment securities available-for-sale	3,691,541	4,093,060
Investment securities held-to-maturity, net	1,068,871	1,111,619
Loans, held for sale	36,658	42,985
Stock in FHLB of Pittsburgh	12,199	24,116
Accrued interest receivable	81,909	74,448
Financial liabilities:
Deposits	15,986,369	16,203,569
Borrowed funds	917,833	726,894
Accrued interest payable	42,481	5,174
Book Value | Level 3
Financial assets:
Other investments	21,741	26,120
Loans and leases, net	12,502,404	11,759,992
Financial liabilities:
Standby letters of credit	663	739
Book Value | Levels 2, 3
Financial assets:
Other assets	203,106	156,993
Financial liabilities:
Other liabilities	211,303	173,622
Fair Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	611,480	837,258
Fair Value | Level 2
Financial assets:
Investment securities available-for-sale	3,691,541	4,093,060
Investment securities held-to-maturity, net	927,680	1,040,104
Loans, held for sale	36,658	42,985
Stock in FHLB of Pittsburgh	12,199	24,116
Accrued interest receivable	81,909	74,448
Financial liabilities:
Deposits	15,951,775	16,156,124
Borrowed funds	917,053	709,014
Accrued interest payable	42,481	5,174
Fair Value | Level 3
Financial assets:
Other investments	21,741	26,120
Loans and leases, net	12,454,772	11,567,888
Financial liabilities:
Standby letters of credit	663	739
Fair Value | Levels 2, 3
Financial assets:
Other assets	203,106	156,993
Financial liabilities:
Other liabilities	$ 211,303	$ 173,622