Fair value measurements (Carrying amounts and fair values of financial instruments) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets
Derivative assets	$ 69,105	$ 48,896
Liabilities
Derivative liabilities (Note 11)	29,321	0
Carrying value
Assets
Cash and cash equivalents	1,204,018	1,659,669
Restricted cash	211,017	364,456
Derivative assets	69,105	48,896
Assets, Carrying value	1,484,140	2,073,021
Liabilities
Debt	29,668,203	28,580,800
Derivative liabilities (Note 11)	29,321
Liabilities, Carrying value	29,697,524	28,580,800
Fair value
Assets
Cash and cash equivalents	1,204,018	1,659,669
Restricted cash	211,017	364,456
Derivative assets	69,105	48,896
Assets, Carrying value	1,484,140	2,073,021
Liabilities
Debt	29,031,153	29,074,375
Derivative liabilities (Note 11)	29,321
Liabilities, Carrying value	29,060,474	29,074,375
Fair value \| Level 1
Assets
Cash and cash equivalents	1,204,018	1,659,669
Restricted cash	211,017	364,456
Derivative assets	0	0
Assets, Carrying value	1,415,035	2,024,125
Liabilities
Debt	0	0
Derivative liabilities (Note 11)	0
Liabilities, Carrying value	0	0
Fair value \| Level 2
Assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Derivative assets	69,105	48,896
Assets, Carrying value	69,105	48,896
Liabilities
Debt	29,031,153	29,074,375
Derivative liabilities (Note 11)	29,321
Liabilities, Carrying value	29,060,474	29,074,375
Fair value \| Level 3
Assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Derivative assets	0	0
Assets, Carrying value	0	0
Liabilities
Debt	0	0
Derivative liabilities (Note 11)	0
Liabilities, Carrying value	$ 0	$ 0

Restricted Cash And Cash Equivalents, Fair Value Disclosure

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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