CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING REVENUES:
Total operating revenues	$ 2,971,963	$ 3,221,679	$ 3,122,592
OPERATING EXPENSES:
Salaries, wages and benefits	1,001,746	1,201,518	1,192,067
Depreciation and amortization	368,098	334,589	292,768
Special items	21,869
Other operating expenses	243,729	272,826	250,778
Total operating expenses	2,459,705	2,747,399	2,734,393
OPERATING INCOME	512,258	474,280	388,199
OTHER INCOME (EXPENSE):
Interest income	14,131	8,823	4,509
Interest expense	(127,755)	(120,409)	(104,925)
Other, net	47,671	3,620	400
Total other expense, net	(65,953)	(107,966)	(100,016)
INCOME BEFORE INCOME TAXES	446,305	366,314	288,183
PROVISION (BENEFIT) FOR INCOME TAXES	106,206	85,942	(140,724)
NET INCOME	$ 340,099	$ 280,372	$ 428,907
BASIC EARNINGS PER SHARE (in dollars per share)	$ 6.68	$ 5.40	$ 8.28
DILUTED EARNINGS PER SHARE (in dollars per share)	$ 6.62	$ 5.30	$ 8.08
Weighted average common shares:
Basic (in shares)	50,932,000	51,914,000	51,804,000
Diluted (in shares)	51,375,000	52,871,000	53,100,000
COMPREHENSIVE INCOME:
Net income	$ 340,099	$ 280,372	$ 428,907
Net unrealized appreciation on marketable securities, net of taxes	32	18	21
TOTAL COMPREHENSIVE INCOME	340,131	280,390	428,928
Flying agreements
OPERATING REVENUES:
Total operating revenues	2,889,265	3,169,520	3,078,297
Airport customer service and other
OPERATING REVENUES:
Total operating revenues	82,698	52,159	44,295
Aircraft maintenance, materials and repairs
OPERATING EXPENSES:
Total operating expenses	514,313	556,259	579,463
Aircraft fuel
OPERATING EXPENSES:
Total operating expenses	119,115	117,657	85,136
Airport related expenses
OPERATING EXPENSES:
Total operating expenses	118,837	109,605	118,374
Aircraft rentals
OPERATING EXPENSES:
Total operating expenses	$ 71,998	$ 154,945	$ 215,807