Valuation and Qualifying Accounts (Details) - Allowance for doubtful receivables [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of year	$ 10,237	$ 4,311
Charged to costs and expenses	3,728	11,025
Write-offs	(3,605)	(5,099)
Transfers, net
Balance at end of year	$ 10,360	$ 10,237