Fair Value Measurements (Details 3) - USD ($) $ in Thousands	Feb. 29, 2020	Dec. 31, 2019
Secured Debt | Significant Other Observable Inputs (Level 2) | Estimate of Fair Value Measurement | ECA Term Financings
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	$ 52,593	$ 150,805
Secured Debt | Significant Other Observable Inputs (Level 2) | Estimate of Fair Value Measurement | Bank Financings
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	1,002,620	1,010,482
Secured Debt | Significant Other Observable Inputs (Level 2) | Reported Value Measurement | ECA Term Financings
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	50,745	147,644
Secured Debt | Significant Other Observable Inputs (Level 2) | Reported Value Measurement | Bank Financings
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	971,693	993,593
Unsecured Debt | Significant Other Observable Inputs (Level 2) | Estimate of Fair Value Measurement | Revolving Credit Facility
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	100,000	150,000
Unsecured Debt | Significant Other Observable Inputs (Level 2) | Reported Value Measurement | Revolving Credit Facility
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	100,000	150,000
Unsecured Debt | Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement | DBJ Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	215,000	215,000
Unsecured Debt | Quoted Prices in Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement | Senior Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	3,807,956	3,787,268
Unsecured Debt | Quoted Prices in Active Markets for Identical Assets (Level 1) | Reported Value Measurement | DBJ Term Loan
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	215,000	215,000
Unsecured Debt | Quoted Prices in Active Markets for Identical Assets (Level 1) | Reported Value Measurement | Senior Notes
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	$ 3,600,000	$ 3,600,000