Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful receivables
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning of Period	$ 1,507	$ 1,429	$ 1,251
Charges to Costs and Expenses	785	541	941
Charges (Deductions) to Other Accounts	(58)	103	(123)
Deductions	(794)	(566)	(640)
End of Period	1,440	1,507	1,429
Tax valuation allowances
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning of Period	5,709	4,903	4,307
Charges to Costs and Expenses	3,859	886	762
Charges (Deductions) to Other Accounts	(192)	394	(140)
Deductions	(3,412)	(474)	(26)
End of Period	$ 5,964	$ 5,709	$ 4,903