FAIR VALUE DISCLOSURES OF FINANCIAL ASSETS AND LIABILITIES - Book Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Financial assets:
Investment securities available-for-sale	$ 4,086,459	$ 4,093,060
Stock in FHLB of Pittsburgh	42,122	24,116
Accrued interest receivable	77,356	74,448
Financial liabilities:
Deposits	16,189,688	16,203,569
Accrued interest payable	15,135	5,174
Book Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	1,103,040	837,258
Book Value | Level 2
Financial assets:
Investment securities available-for-sale	4,086,459	4,093,060
Investment securities held-to-maturity, net	1,094,799	1,111,619
Loans, held for sale	39,734	42,985
Stock in FHLB of Pittsburgh	42,122	24,116
Accrued interest receivable	77,356	74,448
Financial liabilities:
Deposits	16,189,688	16,203,569
Borrowed funds	1,138,206	726,894
Accrued interest payable	15,135	5,174
Book Value | Level 3
Financial assets:
Other investments	24,797	26,120
Loans and leases, net	11,976,845	11,759,992
Financial liabilities:
Standby letters of credit	620	739
Book Value | Levels 2, 3
Financial assets:
Other assets	122,163	156,993
Financial liabilities:
Other liabilities	135,917	173,622
Fair Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	1,103,040	837,258
Fair Value | Level 2
Financial assets:
Investment securities available-for-sale	4,086,459	4,093,060
Investment securities held-to-maturity, net	1,035,856	1,040,104
Loans, held for sale	39,734	42,985
Stock in FHLB of Pittsburgh	42,122	24,116
Accrued interest receivable	77,356	74,448
Financial liabilities:
Deposits	16,147,909	16,156,124
Borrowed funds	1,129,912	709,014
Accrued interest payable	15,135	5,174
Fair Value | Level 3
Financial assets:
Other investments	24,797	26,120
Loans and leases, net	11,955,133	11,567,888
Financial liabilities:
Standby letters of credit	620	739
Fair Value | Levels 2, 3
Financial assets:
Other assets	122,163	156,993
Financial liabilities:
Other liabilities	$ 135,917	$ 173,622