Fair Value Measurements (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Secured Debt | Significant Other Observable Inputs (Level 2) | Reported Value Measurement | Securitization And Term Debt Financing
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	$ (391,680)	$ (828,871)
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	(449,886)	(493,708)
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	(554,888)	(264,256)
Secured Debt | Significant Other Observable Inputs (Level 2) | Estimate of Fair Value Measurement | Securitization And Term Debt Financing
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	(376,752)	(779,901)
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	(471,918)	(506,227)
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	(560,285)	(268,435)
Unsecured Debt | Quoted Prices In Active Markets for Identical Assets (Level 1) | Reported Value Measurement | Revolving Credit Facility [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	(200,000)	0
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	(2,200,000)	(2,150,527)
Unsecured Debt | Quoted Prices In Active Markets for Identical Assets (Level 1) | Estimate of Fair Value Measurement | Revolving Credit Facility [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	(200,000)
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	$ (2,300,615)	$ (2,325,965)