Fair Value Measurements and Derivative Instruments - Recurring (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Assets:
Derivative financial instruments		$ 280,127	$ 215,634
Liabilities:
Derivative financial instruments		7,128	11,210
Fair Value, Measurements, Recurring | Level 1
Assets:
Derivative financial instruments	[1],[2]	0	0
Investments	[2],[3]	5	3,340
Total Assets	[2]	5	3,340
Liabilities:
Derivative financial instruments	[2],[4]	0	0
Total Liabilities	[2]	0	0
Fair Value, Measurements, Recurring | Level 2
Assets:
Derivative financial instruments	[1],[5]	391,116	320,385
Investments	[3],[5]	0	0
Total Assets	[5]	391,116	320,385
Liabilities:
Derivative financial instruments	[4],[5]	118,117	115,961
Total Liabilities	[5]	118,117	115,961
Fair Value, Measurements, Recurring | Level 3
Assets:
Derivative financial instruments	[1],[6]	0	0
Investments	[3],[6]	0	0
Total Assets	[6]	0	0
Liabilities:
Derivative financial instruments	[4],[6]	0	0
Total Liabilities	[6]	0	0
Total | Fair Value, Measurements, Recurring
Assets:
Derivative financial instruments	[1]	391,116	320,385
Investments	[3]	5	3,340
Total Assets		391,121	323,725
Liabilities:
Derivative financial instruments	[4]	118,117	115,961
Total Liabilities		$ 118,117	$ 115,961

[1] Consists of foreign currency forward contracts, interest rate swaps and fuel swaps. Please refer to the “Fair Value of Derivative Instruments” table for breakdown by instrument type.

[2] Inputs based on quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access. Valuation of these items does not entail a significant amount of judgment.

[3] Consists of exchange-traded equity securities and mutual funds reported within Other assets in our consolidated balance sheets.

[4] Consists of foreign currency forward contracts, interest rate swaps and fuel swaps. Please refer to the “Fair Value of Derivative Instruments” table for breakdown by instrument type.

[5] Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. For foreign currency forward contracts, interest rate swaps and fuel swaps, fair value is derived using valuation models that utilize the income valuation approach. These valuation models take into account the contract terms, such as maturity, as well as other inputs, such as foreign exchange rates and curves, fuel types, fuel curves and interest rate yield curves. All derivative instrument fair values take into account the creditworthiness of the counterparty and the Company.

[6] Inputs that are unobservable. The Company did not use any Level 3 inputs as of March 31, 2018 and December 31, 2017.