MARKETABLE SECURITIES - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) Position	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Position security	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Investments Debt And Equity Securities [Abstract]
Other than temporary impairment losses on debt securities related to credit losses	$ 0		$ 0		$ 0
Number of investment positions in an unrealized loss position | Position	45		45
Number of securities other than agencies amount | security			0
Fair value of securities pledged as collateral	$ 267,795,000		$ 267,795,000		$ 259,557,000
Number of held-to-maturity securities sold	0	0	0	0