Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e681-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Financial Instruments and Risk Management - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 aircraft derivative_instrument	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Interest rate derivative losses reclassified into earnings	$ 53	$ 56	$ 160	$ 170
Loss reclassified from AOCI into earnings, tax	31	32	92	97
Accumulated other comprehensive loss	1,214		1,214			$ 1,345
Airbus A321 [Member]
Derivative [Line Items]
Number of aircraft protected by interest rate derivatives schedule for delivery \| aircraft					3
Interest Rate Swap [Member]
Derivative [Line Items]
Number of interest rate derivatives settled \| derivative_instrument					6
Accumulated other comprehensive loss	1,200		1,200			$ 1,300
Interest Rate Swap [Member] \| Cash Flow Hedging [Member]
Derivative [Line Items]
Interest rate derivative losses reclassified into earnings	$ 53	$ 56	$ 160	$ 170