BUSINESS COMBINATIONS - Narrative (Details) $ / shares in Units, $ in Thousands			3 Months Ended
	Feb. 29, 2020	Mar. 01, 2019 USD ($) Branch $ / shares	Mar. 31, 2020 Branch	Jun. 30, 2019 Branch	Dec. 31, 2018 Branch	Jun. 30, 2018 Branch	Mar. 31, 2019 USD ($)
Business Acquisition [Line Items]
Share price (USD per share) | $ / shares		$ 43.28
Securities sold							$ 583,900
Number of offices sold | Branch						11
Beneficial
Business Acquisition [Line Items]
Shares issued per acquire (in shares)		0.3013
Cash paid per acquire (USD per share) | $ / shares		$ 2.93
Stock consideration		$ 949,968
Cash paid to Beneficial stock and option holders		228,239
Value of consideration		$ 1,178,207
Number of branches acquired | Branch		74
Remeasurement period	1 year
Loans and leases, net		$ 3,711,246
Investment securities		619,834
Securities sold		578,800					$ 5,100
Deferred income taxes		18,463
Number of offices sold | Branch			1		14
Number of offices sold during acquisition | Branch				5
Deposit premium percentage				7.37%
Number of branches closed | Branch			2
Beneficial | Core deposits
Business Acquisition [Line Items]
Intangible assets		$ 85,053
Useful life		10 years