Valuation and Qualifying Accounts - Summarized Activity in Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 8,000	$ 7,700	$ 12,700
Additions Charged to Expense	16,000	14,000	12,500
Deductions from the Reserve	(14,000)	(13,700)	(11,300)
Reclassification to Accounts Payable and Accrued Liabilities	0	0	(6,200)	$ 6,200
Balance at End of Year	$ 10,000	$ 8,000	$ 7,700	$ 12,700