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	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Significant non-cash investing and financing activities
Other payable issued for purchased customer accounts	$ (9)	$ 1,547
Estimated acquisition earn-out payables and related charges	14,988	$ 13,978
Common stock issued for agency acquisition	4,892
Notes payable issued or assumed for purchased customer accounts	$ (1,355)