CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
OPERATING REVENUES:
Total operating revenues	$ 805,515	$ 791,512	[1]	$ 1,588,915	$ 1,538,678
OPERATING EXPENSES:
Salaries, wages and benefits	293,677	294,795	[1]	600,396	592,462
Depreciation and amortization	82,714	71,206	[1]	160,298	141,320
Other operating expenses	69,263	62,126	[1]	137,653	124,801
Total operating expenses	678,837	684,916	[1]	1,374,062	1,355,788
OPERATING INCOME	126,678	106,596	[1]	214,853	182,890
OTHER INCOME (EXPENSE):
Interest income	1,705	1,330	[1]	3,409	1,990
Interest expense	(28,811)	(27,063)	[1]	(55,045)	(51,612)
Other income (expense), net	(1,245)			2,313
Total other expense, net	(28,351)	(25,733)	[1]	(49,323)	(49,622)
INCOME BEFORE INCOME TAXES	98,327	80,863	[1]	165,530	133,268
PROVISION FOR INCOME TAXES	22,468	30,386	[1]	35,310	48,005
NET INCOME	$ 75,859	$ 50,477	[1]	$ 130,220	$ 85,263
BASIC EARNINGS PER SHARE (in dollars per share)	$ 1.46	$ 0.98	[1]	$ 2.51	$ 1.65
DILUTED EARNINGS PER SHARE (in dollars per share)	$ 1.43	$ 0.95	[1]	$ 2.46	$ 1.61
Weighted average common shares:
Basic (in shares)	52,046	51,751	[1]	51,983	51,785
Diluted (in shares)	52,913	52,977	[1]	52,973	53,090
COMPREHENSIVE INCOME:
Net income	$ 75,859	$ 50,477	[1]	$ 130,220	$ 85,263
Net unrealized appreciation on marketable securities, net of taxes	84	17	[1]	33	56
TOTAL COMPREHENSIVE INCOME	75,943	50,494	[1]	130,253	85,319
Flying agreements
OPERATING REVENUES:
Total operating revenues	793,637	781,724	[1]	1,561,602	1,516,253
Airport customer service and other
OPERATING REVENUES:
Total operating revenues	11,878	9,788	[1]	27,313	22,425
Aircraft maintenance, materials and repairs
OPERATING EXPENSES:
Total operating expenses	139,774	152,356	[1]	281,380	284,681
Aircraft rentals
OPERATING REVENUES:
Total operating revenues	201,306	208,669		390,375	407,132
OPERATING EXPENSES:
Total operating expenses	37,508	55,413	[1]	82,188	113,123
Aircraft fuel
OPERATING EXPENSES:
Other operating expenses		20,071			38,504
Total operating expenses	25,890	28,949	[1]	55,197	60,897
Airport related expenses
OPERATING EXPENSES:
Other operating expenses		28,949			60,897
Total operating expenses	$ 30,011	$ 20,071	[1]	$ 56,950	$ 38,504

[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 contained in Part I, Item 1 of this report for additional information.