MARKETABLE SECURITIES - Narrative (Details)	3 Months Ended
	Mar. 31, 2019 USD ($) Position security	Mar. 31, 2018 security	Dec. 31, 2018 USD ($)
Investments Debt And Equity Securities [Abstract]
Other than temporary impairment losses on debt securities related to credit losses | $	$ 0		$ 0
Number of investment positions in an unrealized loss position | Position	96
Number of securities other than agencies amount | security	0
Fair value of securities pledged as collateral | $	$ 278,137,000		$ 259,557,000
Number of securities sold | security	0	0