BUSINESS COMBINATIONS - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Mar. 01, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Liabilities assumed:
Goodwill resulting from acquisition of Beneficial		$ 472,958		$ 166,007
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	619,853
Loans and leases, net	3,711,246
Premises and equipment	69,873
Deferred income taxes	18,485
Bank owned life insurance	82,510
Other assets	135,862
Total assets	5,029,659
Liabilities assumed:
Deposits	4,056,506
Other liabilities	101,897
Total liabilities	4,158,403
Net assets acquired:	871,256
Goodwill resulting from acquisition of Beneficial	306,951	$ 306,951	$ 309,486
Core deposits | Beneficial
Assets acquired:
Intangible assets	85,053
Loan servicing rights | Beneficial
Assets acquired:
Intangible assets	$ 2,466