Schedule II Valuation and Qualifying Accounts and Reserves Supplemental Schedule (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts receivable reserves
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 1,858	$ 2,066	$ 2,121
Charged to Costs and Expenses	1,874	1,155	795
Charged to Other Accounts	0	(91)	39
Deductions	(931)	(797)	(889)
Balance at End of Period	2,801	2,333	2,066
Accounts receivable reserves | Difference between Revenue Guidance in Effect before and after Topic 606
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	475
Deferred tax assets valuation allowance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1,733	85	85
Charged to Costs and Expenses	14	1,648	0
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	$ 1,747	$ 1,733	$ 85