Commitments and Contingencies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Land_Parcel	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Long-term Purchase Commitment [Line Items]
Aircraft and real estate rental expense	$ 49,319	$ 53,581	$ 53,718
Aggregate amount of guarantees and bonds	1,000
Total aircraft deposits	501	$ 4,818
Aggregate estimated probable liability environmental matters	$ 150
Number of parcels of land exists | Land_Parcel	2
2018 [Member]
Long-term Purchase Commitment [Line Items]
Aggregate purchase price for aircraft	$ 127,000
2019 [Member]
Long-term Purchase Commitment [Line Items]
Aggregate purchase price for aircraft	129,000
2020 [Member]
Long-term Purchase Commitment [Line Items]
Aggregate purchase price for aircraft	$ 22,700