CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 345,854	$ 215,723
Marketable securities	609,821	610,185
Receivables, net	55,908	34,462
Inventories, net	97,987	91,196
Other current assets	21,263	31,236
Total current assets	1,130,833	982,802
PROPERTY AND EQUIPMENT:
Aircraft and rotable spares	7,613,584	7,527,555
Deposits on aircraft	90,044	31,625
Buildings and ground equipment	252,638	258,863
Total property and equipment, gross	7,956,266	7,818,043
Less-accumulated depreciation and amortization	(2,671,940)	(2,455,995)
Total property and equipment, net	5,284,326	5,362,048
OTHER ASSETS:
Operating lease right-of-use assets	262,172	282,362
Long-term receivables and other assets	314,432	260,410
Total other assets	576,604	542,772
Total assets	6,991,763	6,887,622
CURRENT LIABILITIES:
Current maturities of long-term debt	360,968	402,158
Accounts payable	299,757	278,677
Accrued salaries, wages and benefits	141,842	125,944
Current maturities of operating lease liabilities	78,289	82,641
Taxes other than income taxes	28,505	26,183
Other current liabilities	199,997	26,119
Total current liabilities	1,109,358	941,722
LONG-TERM DEBT, net of current maturities	2,652,262	2,801,538
DEFERRED INCOME TAXES PAYABLE	656,259	625,931
NONCURRENT OPERATING LEASE LIABILITIES	187,860	205,845
OTHER LONG-TERM LIABILITIES	137,119	173,041
COMMITMENTS AND CONTINGENCIES (Note 7)
STOCKHOLDERS' EQUITY:
Preferred stock, 5,000,000 shares authorized; none issued
Common stock, no par value, 120,000,000 shares authorized; 82,301,551 and 82,094,985 shares issued as of June 30, 2021 and December 31, 2020, respectively	717,714	704,675
Retained earnings	2,149,900	2,052,006
Treasury stock, at cost, 31,955,991 and 31,913,635 shares as of June 30, 2021 and December 31, 2020, respectively	(618,709)	(617,136)
Total stockholders' equity	2,248,905	2,139,545
Total liabilities and stockholders' equity	$ 6,991,763	$ 6,887,622