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Quarterly Financial Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]                      
Operating revenues $ 492,297 $ 598,452 $ 675,765 $ 704,171 $ 795,937 $ 867,478 $ 854,418 $ 809,164 $ 2,470,685 $ 3,326,997 $ 2,356,684
Operating income (loss) (82,763) (307,305) (48,125) (23,383) (210,790) (80,281) (9,004) (22,102) (461,576) (322,177) (292,538)
Net income (loss) $ (85,923) $ (261,719) $ (49,447) $ (28,614) $ (201,249) $ (75,042) $ (10,713) $ (34,417) $ (425,703) $ (321,421) $ 5,910
Net loss per common share:                      
Basic $ (0.44) $ (1.31) $ (0.24) $ (0.14) $ (0.93) $ (0.34) $ (0.05) $ (0.16) $ (2.10) $ (1.47) $ 0.03
Diluted $ (0.44) $ (1.31) $ (0.24) $ (0.14) $ (0.93) $ (0.34) $ (0.05) $ (0.16) $ (2.10) $ (1.47) $ 0.03