Income and Partnership Taxes Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for taxes		$ 42,789	$ 34,743	$ 1,112
Provision for the PTP tax		12,100	11,600	11,100
Provision (benefit) pertaining to corporate subsidiaries		30,659	23,143	(9,998)
Valuation allowance	$ 6,410	6,606	6,410
Foreign tax credit carryforwards available for U.S. federal income tax purposes	8,758	7,439	8,758
Valuation allowance	2,300	196	2,321	(119)
Tax Cuts and Jobs Act of 2017, income tax expense (benefit)			(8,600)	(6,100)
Tax Cuts and Jobs Act of 2017, deferred tax liability, existing income tax benefit			1,300	49,200
Change in U.S. tax law		111	(8,730)	$ (54,171)
Tax attribute carryforwards	2,321	2,101	2,321
Deferred tax liabilities, OCI	$ 500	$ 2,600	$ 500