RELATED-PARTY TRANSACTIONS - Incentive Compensation (Details) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Vidler Incentive Compensation Plan
Related Party Transaction [Line Items]
Employee benefits and share-based compensation	$ 414,000	$ 0	$ 0

Amount of cost (reversal of cost) for employee benefits and share-based payment arrangement. Includes, but is not limited to, pension, other postretirement, postemployment and termination benefits.

No definition available.

Name:	us-gaap_EmployeeBenefitsAndShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration