Supplemental Disclosures of Cash Flow Information and Non-Cash Financing and Investing Activities - Summary of Significant Non-Cash Investing and Financing Activities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Significant non-cash investing and financing activities
Other payables issued for agency acquisitions and purchased customer accounts	$ 15,072	$ 9,130	$ 12,135
Estimated acquisition earn-out payables and related charges	75,761	131,397	82,872
Contingent payable issued for agency acquisition	24,114	0	0
Common stock issued for agency acquisition	9,892	0	0
Notes payable assumed for agency acquisition	1,355	0	0
Notes received on the sale of fixed assets and customer accounts	$ 0	$ 0	$ 9,903