Income and Partnership Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Provision (benefit) for taxes	$ (137,915)	$ 42,789	$ 34,743
Provision for the PTP tax	2,500	12,100	11,600
Provision (benefit) pertaining to corporate subsidiaries	(140,393)	30,659	23,143
Tax attribute carryforwards	13,224	2,101
Operating loss carryforwards, valuation allowance	200
Foreign tax credit carryforwards available for U.S. federal income tax purposes	8,765	7,439
Valuation allowance	9,755	6,606
Valuation allowance, deferred tax asset, increase (decrease)	3,100
Income taxes receivable, CARES Act	55,400
Income tax benefit, carry back, CARES Act	18,100
Incremental tax benefit, CARES Act	34,200
Change in deferred tax assets valuation allowance, CARES Act	(16,100)
Additional income taxes receivable	11,900
Tax Cuts and Jobs Act of 2017, income tax benefit			8,600
Tax Cuts and Jobs Act of 2017, deferred tax liability, existing income tax benefit			1,300
Change in enacted tax rate	(17,983)	111	$ (8,730)
Deferred tax liabilities, OCI	3,200	$ 2,600
Expiration of Foreign Tax Credits
Operating Loss Carryforwards [Line Items]
Valuation allowance, deferred tax asset, increase (decrease)	(2,300)
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Tax attribute carryforwards	13,000
Operating loss carryforwards, valuation allowance	8,200
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Valuation allowance	1,600
Valuation allowance, deferred tax asset, increase (decrease)	$ (5,100)