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Significant Transactions - NSM (Details) £ in Millions						3 Months Ended		9 Months Ended
	Apr. 07, 2020 USD ($)	Apr. 07, 2020 GBP (£)	Mar. 31, 2019 USD ($)	Dec. 03, 2018 USD ($)	May 18, 2018 USD ($) earnout_period	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($)	Apr. 07, 2020 GBP (£)
Other Significant Noncash Transactions [Line Items]
(Loss) gain on sale						$ 28,700,000
Goodwill						613,400,000			$ 525,500,000
Change in fair value of contingent consideration earnout liabilities						0	$ (600,000)
Change in Fair Value of Contingent Earnout Liability, Expense (Revenue) Recognized						0	(600,000)
Payment for Contingent Consideration Liability, Financing Activities						6,700,000	6,400,000
NSM Insurance HoldCo, LLC
Other Significant Noncash Transactions [Line Items]
Cash consideration to acquire businesses and interest in affiliates				$ 29,000,000.0
Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)					100.00%
Equity method investment, aggregate cost					$ 49,600,000
Borrowings					$ 51,000,000.0
Purchase price adjustment								$ 700,000
Number of earnout periods | earnout_period					2
KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Other Significant Noncash Transactions [Line Items]
Cash consideration to acquire businesses and interest in affiliates				60,000,000.0
Borrowings				$ 30,100,000
Goodwill			$ 32,600,000
Intangible assets acquired			32,700,000
Specialty Insurance Distribution (NSM)
Other Significant Noncash Transactions [Line Items]
Contingent consideration earnout liabilities						7,900,000			$ 14,600,000
Specialty Insurance Distribution (NSM) | Kingsbridge Group Limited
Other Significant Noncash Transactions [Line Items]
Equity method investment, aggregate cost	$ 132,200,000									£ 107.2
Borrowings	$ 52,400,000	£ 42.5
Percentage of voting interests acquired	100.00%									100.00%
Stock issued during period, value, acquisitions	$ 80,300,000
Acquisitions of businesses	111,500,000
Attribution of acquisition date fair value estimates between goodwill and other intangible assets	20,200,000
Contingent consideration related to the Ark Transaction	4,100,000					200,000
Pretax income	4,100,000
Foreign currency translation gain	$ 300,000
NSM Bank Facility | Specialty Insurance Distribution (NSM)
Other Significant Noncash Transactions [Line Items]
Amount borrowed						$ 277,300,000
NSM Insurance HoldCo, LLC
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)						96.60%
Fully diluted ownership interest (as a percent)						89.60%
KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Other Significant Noncash Transactions [Line Items]
Change in fair value of contingent consideration earnout liabilities			$ 5,900,000
Payment for Contingent Consideration Liability, Financing Activities						$ 6,700,000	$ 6,400,000
KBK Insurance Group, Inc. & KBK Premium Services, Inc. | Specialty Insurance Distribution (NSM)
Other Significant Noncash Transactions [Line Items]
Contingent consideration earnout liabilities						$ 6,400,000

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