Contract Balances - Valuation And Qualifying Accounts Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Contract Balances
Allowance for Doubtful Accounts Receivable, Beginning Balance	$ 16,966	$ 15,511	$ 18,399
Charged to Costs and Expenses	69,866	98,575	124,126
Deductions	67,552	97,120	127,014
Allowance for Doubtful Accounts Receivable, Ending Balance	$ 19,280	$ 16,966	$ 15,511