SECURITIES AVAILABLE FOR SALE - Securities Impairment (Details) - Available-for-sale Securities - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Estimated credit losses as of prior year-end	$ 1,697	$ 1,697	$ 1,697	$ 1,697
Reductions for securities paid off during the period	0	0	0	0
Estimated credit losses at end of the period	$ 1,697	$ 1,697	$ 1,697	$ 1,697