CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	[1]	Dec. 31, 2016
OPERATING REVENUES:
Total operating revenues		$ 3,221,679	$ 3,122,592		$ 3,063,702	[1]
OPERATING EXPENSES:
Salaries, wages and benefits		1,201,518	1,192,067		1,205,459	[1]
Depreciation and amortization		334,589	292,768		284,969	[1]
Special items	[1]				465,649
Other operating expenses		272,826	250,778		255,559	[1]
Total operating expenses		2,747,399	2,734,393		3,236,386	[1]
OPERATING INCOME (LOSS)		474,280	388,199		(172,684)	[1]
OTHER INCOME (EXPENSE):
Interest income		8,823	4,509		2,143	[1]
Interest expense		(120,409)	(104,925)		(78,177)	[1]
Other, net		3,620	400		(94)	[1]
Total other expense, net		(107,966)	(100,016)		(76,128)	[1]
INCOME (LOSS) BEFORE INCOME TAXES		366,314	288,183		(248,812)	[1]
PROVISION (BENEFIT) FOR INCOME TAXES		85,942	(140,724)		(87,226)	[1]
NET INCOME (LOSS)		$ 280,372	$ 428,907		$ (161,586)	[1]
BASIC EARNINGS (LOSS) PER SHARE (in dollars per share)		$ 5.40	$ 8.28		$ (3.14)	[1]
DILUTED EARNINGS (LOSS) PER SHARE (in dollars per share)		$ 5.30	$ 8.08		$ (3.14)	[1]
Weighted average common shares:
Basic (in shares)		51,914	51,804		51,505	[1]
Diluted (in shares)		52,871	53,100		51,505	[1]
COMPREHENSIVE INCOME (LOSS):
Net income (loss)		$ 280,372	$ 428,907		$ (161,586)	[1]
Net unrealized appreciation on marketable securities, net of taxes		18	21		189	[1]
TOTAL COMPREHENSIVE INCOME (LOSS)		280,390	428,928		(161,397)	[1]
Flying agreements
OPERATING REVENUES:
Total operating revenues		3,169,520	3,078,297		3,010,738	[1]
Airport customer service and other
OPERATING REVENUES:
Total operating revenues		52,159	44,295		52,964	[1]
Aircraft maintenance, materials and repairs
OPERATING EXPENSES:
Total operating expenses		556,259	579,463		569,306	[1]
Aircraft rentals
OPERATING EXPENSES:
Total operating expenses		154,945	215,807		262,602	[1]
Aircraft fuel
OPERATING EXPENSES:
Total operating expenses		117,657	85,136		70,701	[1]
Airport related expenses
OPERATING EXPENSES:
Total operating expenses		$ 109,605	$ 118,374		$ 122,141	[1]

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606). See Note 1 to the financial statements of this report for additional information.