Quarterly Financial Data (Unaudited) (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) $ / shares shares	Mar. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares item shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
Quarterly Financial Data (Unaudited)
Operating revenues	$ 758,017	$ 799,776	$ 801,338	$ 762,075	$ 752,744	$ 794,004	$ 788,417	$ 760,398	$ 3,121,206	$ 3,095,563	$ 3,237,447
Operating income	(404,464)	85,834	84,137	61,809	52,212	78,296	69,932	34,075	(172,684)	234,515	24,848
Net income (loss)	$ (270,244)	$ 41,322	$ 40,244	$ 27,092	$ 40,454	$ 36,268	$ 31,475	$ 9,620	$ (161,586)	$ 117,817	$ (24,154)
Net income (loss) per common share:
Basic (in dollars per share) | $ / shares	$ (5.22)	$ 0.80	$ 0.78	$ 0.53	$ 0.80	$ 0.72	$ 0.61	$ 0.19	$ (3.14)	$ 2.31	$ (0.47)
Diluted (in dollars per share) | $ / shares	$ (5.22)	$ 0.79	$ 0.77	$ 0.52	$ 0.78	$ 0.71	$ 0.61	$ 0.18	$ (3.14)	$ 2.27	$ (0.47)
Weighted average common shares:
Basic (in shares) | shares	51,757	51,627	51,418	51,218	50,880	50,616	51,357	51,457	51,505	51,077	51,237
Diluted (in shares) | shares	51,757	52,471	52,194	52,014	51,657	51,282	51,971	52,392	51,505	51,825	51,237
Special Charge									$ 465,649		$ 74,777
Number of seats on aircraft | item									50