CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
OPERATING REVENUES:
Total operating revenues	$ 744,383	$ 805,515	$ 1,468,077	$ 1,588,915
OPERATING EXPENSES:
Salaries, wages and benefits	243,766	293,677	501,354	600,396
Depreciation and amortization	90,148	82,714	180,134	160,298
Special items			21,869
Other operating expenses	61,948	69,263	125,057	137,653
Total operating expenses	600,290	678,837	1,227,565	1,374,062
OPERATING INCOME	144,093	126,678	240,512	214,853
OTHER INCOME (EXPENSE):
Interest income	3,731	1,705	7,538	3,409
Interest expense	(32,770)	(28,811)	(65,278)	(55,045)
Other income (expense), net	281	(1,245)	47,006	2,313
Total other expense, net	(28,758)	(28,351)	(10,734)	(49,323)
INCOME BEFORE INCOME TAXES	115,335	98,327	229,778	165,530
PROVISION FOR INCOME TAXES	27,283	22,468	53,545	35,310
NET INCOME	$ 88,052	$ 75,859	$ 176,233	$ 130,220
BASIC EARNINGS PER SHARE (in dollars per share)	$ 1.72	$ 1.46	$ 3.44	$ 2.51
DILUTED EARNINGS PER SHARE (in dollars per share)	$ 1.71	$ 1.43	$ 3.40	$ 2.46
Weighted average common shares:
Basic (in shares)	51,145	52,046	51,293	51,983
Diluted (in shares)	51,477	52,913	51,787	52,973
COMPREHENSIVE INCOME:
Net income	$ 88,052	$ 75,859	$ 176,233	$ 130,220
Net unrealized appreciation on debt securities, net of taxes		84	32	33
TOTAL COMPREHENSIVE INCOME	88,052	75,943	176,265	130,253
Flying agreements
OPERATING REVENUES:
Total operating revenues	725,335	793,637	1,425,336	1,561,602
Airport customer service and other
OPERATING REVENUES:
Total operating revenues	19,048	11,878	42,741	27,313
Aircraft maintenance, materials and repairs
OPERATING REVENUES:
Total operating revenues	124,789	139,774	243,051	281,380
Airport related expenses
OPERATING REVENUES:
Total operating revenues	30,782	25,890	61,429	55,197
Aircraft fuel
OPERATING REVENUES:
Total operating revenues	30,851	30,011	56,507	56,950
Aircraft rentals
OPERATING REVENUES:
Total operating revenues	$ 18,006	$ 37,508	$ 38,164	$ 82,188