Valuation and Qualifying Accounts - Summarized Activity in Allowances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 12,700	$ 7,400	$ 6,900
Additions Charged to Expense	12,500	16,600	4,750
Additions Charged Against Revenues	0	5,500	4,850
Deductions from Reserve	(11,300)	(16,800)	(9,100)
Reclassification to Accounts Payable and Accrued Liabilities	(6,200)
Balance at End of Year	$ 7,700	$ 12,700	$ 7,400