Accumulated Other Comprehensive Income (Loss) - Reclassifications (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Amounts reclassified from AOCI
Passenger revenue	$ (559,144)	$ (656,751)
Nonoperating Income (Expense), Other, net	(2,304)	1,025
Total before tax	175,188	(48,959)
Tax expense	(30,816)	12,601
Total, net of tax	144,372	(36,358)
Net income	144,372	(36,358)
Amount reclassified from accumulated other comprehensive income (loss)
Amounts reclassified from AOCI
Net income	(2,188)	(551)
Derivative instruments under ASC 815 | Amount reclassified from accumulated other comprehensive income (loss)
Amounts reclassified from AOCI
Total before tax	(3,900)	(1,587)
Tax expense	965	391
Total, net of tax	(2,935)	(1,196)
Defined benefit plan | Amount reclassified from accumulated other comprehensive income (loss)
Amounts reclassified from AOCI
Total before tax	978	887
Tax expense	(242)	(168)
Total, net of tax	736	719
Actuarial loss | Amount reclassified from accumulated other comprehensive income (loss)
Amounts reclassified from AOCI
Nonoperating Income (Expense), Other, net	922	831
Prior service cost | Amount reclassified from accumulated other comprehensive income (loss)
Amounts reclassified from AOCI
Nonoperating Income (Expense), Other, net	56	56
Short-term investments | Amount reclassified from accumulated other comprehensive income (loss)
Amounts reclassified from AOCI
Realized losses (gain) on sales of investments, net	14	(98)
Total before tax	14	(98)
Tax expense	(3)	24
Total, net of tax	11	(74)
Passenger
Amounts reclassified from AOCI
Passenger revenue	(503,469)	(601,304)
Passenger | Derivative instruments under ASC 815 | Amount reclassified from accumulated other comprehensive income (loss) | Foreign currency derivative gains, net
Amounts reclassified from AOCI
Passenger revenue	(1,114)	(1,587)
Nonoperating Income (Expense), Other, net	$ 2,786	$ 0