Business Combinations - Estimated Fair Values of Aggregate Assets and Liabilities Acquired (Details) $ in Thousands	Sep. 30, 2021 USD ($)
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash	$ 46,134
Other current assets	52,952
Fixed assets	586
Goodwill	176,658
Other assets	394
Total assets acquired	363,588
Other current liabilities	(76,713)
Deferred income tax, net	(5,057)
Other liabilities	(13)
Total liabilities assumed	(81,783)
Net assets acquired	281,805
O'Leary Insurances (O'Leary)
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash	45,441
Other current assets	43,354
Fixed assets	544
Goodwill	84,649
Other assets	135
Total assets acquired	215,401
Other current liabilities	(72,683)
Deferred income tax, net	(5,057)
Other liabilities	(13)
Total liabilities assumed	(77,753)
Net assets acquired	137,648
Piper Jordan LLC (Piper)
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	2,397
Fixed assets	9
Goodwill	40,019
Total assets acquired	54,679
Net assets acquired	54,679
Berkshire Insurance Group, Inc. (Berkshire)
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	1,621
Fixed assets	9
Goodwill	27,563
Total assets acquired	41,517
Other current liabilities	(17)
Total liabilities assumed	(17)
Net assets acquired	41,500
AGIS Network Inc. (AGIS)
Fair Value Of Assets And Liabilities Statement [Line Items]
Other current assets	520
Fixed assets	20
Goodwill	21,888
Total assets acquired	36,056
Net assets acquired	36,056
Other Acquisitions
Fair Value Of Assets And Liabilities Statement [Line Items]
Cash	693
Other current assets	5,060
Fixed assets	4
Goodwill	2,539
Other assets	259
Total assets acquired	15,935
Other current liabilities	(4,013)
Total liabilities assumed	(4,013)
Net assets acquired	11,922
Purchased Customer Accounts
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	85,853
Purchased Customer Accounts | O'Leary Insurances (O'Leary)
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	40,459
Purchased Customer Accounts | Piper Jordan LLC (Piper)
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	12,233
Purchased Customer Accounts | Berkshire Insurance Group, Inc. (Berkshire)
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	12,313
Purchased Customer Accounts | AGIS Network Inc. (AGIS)
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	13,577
Purchased Customer Accounts | Other Acquisitions
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	7,271
Non-compete Agreements
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	1,011
Non-compete Agreements | O'Leary Insurances (O'Leary)
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	819
Non-compete Agreements | Piper Jordan LLC (Piper)
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	21
Non-compete Agreements | Berkshire Insurance Group, Inc. (Berkshire)
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	11
Non-compete Agreements | AGIS Network Inc. (AGIS)
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	51
Non-compete Agreements | Other Acquisitions
Fair Value Of Assets And Liabilities Statement [Line Items]
Intangible assets	$ 109