BUSINESS COMBINATIONS - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Mar. 01, 2019	Mar. 31, 2020	Feb. 29, 2020	Dec. 31, 2019	Mar. 31, 2019
Liabilities assumed:
Goodwill resulting from acquisition of Beneficial		$ 472,828		$ 472,828
Beneficial
Business Acquisition [Line Items]
Common shares issued (21,816,355)	$ 949,968
Number of shares issued (in shares)	21,816,355
Cash paid to Beneficial stock and option holders	$ 228,239
Value of consideration	1,178,207
Assets acquired:
Cash and due from banks	304,311
Investment securities	619,834
Loans and leases, net	3,711,246
Premises and equipment	69,873
Deferred income taxes	18,463
Bank owned life insurance	82,510
Other assets	135,890
Total assets	5,029,646
Liabilities assumed:
Deposits	4,056,506
Other liabilities	101,754
Total liabilities	4,158,260
Net assets acquired:	871,386
Goodwill resulting from acquisition of Beneficial	306,821		$ 306,821		$ 309,486
Core deposits | Beneficial
Assets acquired:
Intangible assets	85,053
Loan servicing rights | Beneficial
Assets acquired:
Intangible assets	$ 2,466