BASIS OF PRESENTATION AND ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) branch	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jan. 01, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of branches operated | branch	114
Reserve requirement	$ 52,700		$ 61,200
Initial recognition of operating lease right-of-use assets	25,739
Initial recognition of operating lease liabilities	$ 28,080
Cumulative effect of change in accounting principle		$ 276		$ (28)
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Initial recognition of operating lease right-of-use assets		27,300
Initial recognition of operating lease liabilities		29,700
Cumulative effect of change in accounting principle		$ 276
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	7 years
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	10 years
US Premium Financing Holding Company | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	3 years
US Premium Financing Holding Company | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	8 years