RELATED PERSON TRANSACTIONS - Transactions with our Controlling Shareholders (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Lease Services \| Entities owned by the controlling shareholders
Related Party Transaction [Line Items]
Lease payments made to entities	$ 1.4	$ 1.4
Charter Aircraft \| Controlling shareholders \| Maximum
Related Party Transaction [Line Items]
Aircraft expenses	$ 0.4	$ 0.5

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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