EMPLOYEE BENEFIT PLAN - Trading results related to SERP (Details 1) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Non-qualified Supplemental Retirement Plan ("SERP")
Defined Benefit Plan Disclosure [Line Items]
Trading gains (losses), net	$ 428	$ 977	$ 1,981	$ 713

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration