SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - INTANGIBLE ASSETS AND SEGMENTS (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) segment
Income Taxes
Tax benefit | $	$ 0.0
Operating Segments
Number of reportable operating segments | segment	1
Minimum
Income Taxes
Useful life of core deposit intangible assets	10 years
Maximum
Income Taxes
Useful life of core deposit intangible assets	15 years