Schedule II - Valuation and qualifying accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for Doubtful Accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ (893)	$ (840)	$ (892)
Additions Charged to Costs and Expenses	(607)	(83)	(376)
Deduction	203	30	428
Balance at End of Year	(1,297)	(893)	(840)
Tax Valuation Allowance
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	(1,603)	(1,363)	(1,225)
Additions Charged to Costs and Expenses	(378)	(240)	(138)
Deduction	0	0	0
Balance at End of Year	$ (1,981)	$ (1,603)	$ (1,363)