Long-term investments - Investments in Significant Partnerships and Joint Ventures (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Assets	$ 11,188,028	$ 10,911,470
Liabilities	6,332,841	6,173,099
APUC's investment carrying amount for the entities	119,798	83,497
Investments in Significant Partnerships and Joint Ventures
Schedule of Equity Method Investments [Line Items]
Assets	1,686,942	833,791
Liabilities	1,496,166	697,751
Net assets	190,776	136,040
Investments in Significant Partnerships and Joint Ventures \| APUC
Schedule of Equity Method Investments [Line Items]
Net assets	98,645	63,624
Difference between investment carrying amount and underlying equity in net assets(a)	21,153	18,487
APUC's investment carrying amount for the entities	$ 119,798	$ 82,111

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

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Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future.

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