Schedule II - Valuation and qualifying accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ (1,297)	$ (893)	$ (840)
Additions Charged to Costs and Expenses	(404)	(607)	(83)
Deduction	322	203	30
Additions due to acquisitions	(208)	0	0
Balance at End of Year	(1,587)	(1,297)	(893)
Tax Valuation Allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	(1,981)	(1,603)	(1,363)
Additions Charged to Costs and Expenses	(1,805)	(378)	(240)
Deduction	0	0	0
Balance at End of Year	$ (3,786)	$ (1,981)	$ (1,603)