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LONG-TERM DEBT - LINE OF CREDIT (Details) | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2017 USD ($) credit_facility | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Line of Credit Facility [Line Items] |  |  |  |  |
Line of credit facility, borrowing capacity | $ 475,000,000 |  |  |  |
Number of credit facilities | credit_facility | 3 |  |  |  |
Credit Facility 1 [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Line of credit facility, asset restrictions, unrestricted cash and marketable securities | $ 500,000,000 |  |  |  |
Credit Facility 1 [Member] | Secured by aircraft [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Line of credit facility, borrowing capacity |  |  | $ 250,000,000 | $ 100,000,000 |
Line of Credit Facility, Expiration Date | Jun. 30, 2021 |  |  |  |
Number of credit facilities | credit_facility | 1 |  |  |  |
Credit Facility 2 [Member] | Secured by other [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Line of credit facility, borrowing capacity |  |  |  | $ 150,000,000 | $ 100,000,000
Line of Credit Facility, Expiration Date | Mar. 31, 2022 |  |  |  |
Credit Facility 3 [Member] | Secured by aircraft [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Line of credit facility, borrowing capacity |  | $ 75,000,000 | $ 52,000,000 |  |
Line of Credit Facility, Expiration Date | Sep. 30, 2018 |  |  |  |
Credit Facilities 1 and 2 [Member] |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |
Number of credit facilities, no borrowing | credit_facility | 2 |  |  |  |

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- Definition Line of Credit Facility, Asset Restrictions, Unrestricted Cash and Marketable Securities + References No definition available. + Details
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Balance Type: | debit
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- Definition Line of Credit Facility, Number of Credit Facilities + References No definition available. + Details
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- Definition Line of Credit Facility, Number of Credit Facilities, No Borrowing + References No definition available. + Details
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- Definition Date the credit facility terminates, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition 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. + References No definition available. + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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Balance Type: | credit
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- Details
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- Details
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- Details
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- Details
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