Summary of significant accounting policies - Changes In Accounting Standard Updates (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability	$ 199,571
Operating lease right-of-use-assets	199,171
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability		$ 257,000
Operating lease right-of-use-assets		257,000
Hawaiian Electric Company, Inc. and Subsidiaries
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use-assets	$ 176,809
Hawaiian Electric Company, Inc. and Subsidiaries | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability		236,000
Operating lease right-of-use-assets		236,000
Power Purchase Agreement | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability		215,000
Operating lease right-of-use-assets		$ 215,000