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Variable Interest Entity and Noncontrolling Interests - Variable interest entity (Details) - USD ($) $ in Millions	1 Months Ended
	Mar. 31, 2014	Jul. 01, 2021
Greysbridge Holdings Ltd
Variable Interest Entity [Line Items]
Percentage ownership		40.00%
Greysbridge Holdings Ltd \| Kelso And Company
Variable Interest Entity [Line Items]
Percentage ownership		30.00%
Greysbridge Holdings Ltd \| Warburg Pincus LLC
Variable Interest Entity [Line Items]
Percentage ownership		30.00%
Variable Interest Entity, Primary Beneficiary \| Somers Holdings Ltd.
Variable Interest Entity [Line Items]
Initial investment contribution amount	$ 100
Variable Interest Entity, Primary Beneficiary \| Common shares \| Somers Holdings Ltd.
Variable Interest Entity [Line Items]
Number of shares acquired	2,500,000