BASIS OF PRESENTATION AND ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) branch	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reserve requirement	$ 46,000		$ 44,100
Number of branches operated | branch	97
Stranded tax effects			$ 392
Reclassification to retained earnings due to change in federal corporate tax rate	$ (392)
Accumulated Other Comprehensive Income (Loss), Net of Tax
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification to retained earnings due to change in federal corporate tax rate	(392)	$ 0
Accumulated Other Comprehensive Income (Loss), Net of Tax | Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification to retained earnings due to change in federal corporate tax rate	(392)
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification to retained earnings due to change in federal corporate tax rate	392	$ 0
Retained Earnings | Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification to retained earnings due to change in federal corporate tax rate	$ 392