Operating Segments and Related Disclosures - Geographic Revenues (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenue	$ 578,351	$ 621,329	$ 584,133	$ 538,143	$ 519,846	$ 574,841	$ 553,421	$ 493,355	$ 2,321,956	$ 2,141,463	$ 1,931,580
DOT—Domestic
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenue									2,136,200	1,940,200	1,728,800
DOT—Latin America
Revenues from External Customers and Long-Lived Assets [Line Items]
Operating revenue									$ 185,800	$ 201,300	$ 202,800