FAIR VALUE DISCLOSURES OF FINANCIAL ASSETS AND LIABILITIES - Book Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financial assets:
Investment securities available-for-sale	$ 5,495,929	$ 5,205,311
Loans and leases, net	11,197,482	7,791,482
Stock in FHLB of Pittsburgh	8,804	6,073
Accrued interest receivable	53,241	41,596
Financial liabilities:
Deposits	17,623,544	13,240,062
Accrued interest payable	5,258	736
Book Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	2,283,769	1,532,939
Book Value | Levels 2, 3
Financial liabilities:
Other liabilities	89,148	23,291
Book Value | Level 2
Financial assets:
Investment securities available-for-sale	5,495,929	5,205,311
Investment securities held-to-maturity, net	84,898	90,642
Loans, held for sale	70,617	113,349
Stock in FHLB of Pittsburgh	8,804	6,073
Accrued interest receivable	53,241	41,596
Other assets	72,461	5,153
Financial liabilities:
Deposits	17,623,544	13,240,062
Borrowed funds	372,402	239,477
Accrued interest payable	5,258	736
Book Value | Level 3
Financial assets:
Other investments	13,651	10,518
Loans and leases, net	11,197,482	7,791,482
Financial liabilities:
Standby letters of credit	413	674
Fair Value | Level 1
Financial assets:
Cash, cash equivalents, and restricted cash	2,283,769	1,532,939
Fair Value | Levels 2, 3
Financial liabilities:
Other liabilities	89,148	23,291
Fair Value | Level 2
Financial assets:
Investment securities available-for-sale	5,495,929	5,205,311
Investment securities held-to-maturity, net	85,754	94,131
Loans, held for sale	70,617	113,349
Stock in FHLB of Pittsburgh	8,804	6,073
Accrued interest receivable	53,241	41,596
Other assets	72,461	5,153
Financial liabilities:
Deposits	17,603,155	13,236,816
Borrowed funds	350,649	225,119
Accrued interest payable	5,258	736
Fair Value | Level 3
Financial assets:
Other investments	13,651	10,518
Loans and leases, net	11,355,608	7,723,867
Financial liabilities:
Standby letters of credit	$ 413	$ 674