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, 2020	Dec. 31, 2019	Dec. 31, 2018
Significant non-cash investing and financing activities
Other payables issued for purchased customer accounts	$ 9,130	$ 12,135	$ 5,462
Estimated acquisition earn-out payables and related charges	$ 131,397	82,872	77,378
Notes received on the sale of fixed assets and customer accounts		$ 9,903	$ 52