Schedule II - Valuation and qualifying accounts (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ (840)		$ (892)		$ (464)
Additions Charged to Costs and Expenses	(83)	[1]	(376)	[1]	(545)	[1]
Deduction	30	[2]	428	[2]	117	[2]
Balance at End of Year	(893)		(840)		(892)
Valuation Allowance of Deferred Tax Assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	(1,363)		(1,225)		(361)
Additions Charged to Costs and Expenses	(240)	[3]	(138)	[3]	(864)	[3]
Deduction	0		0		0
Balance at End of Year	$ (1,603)		$ (1,363)		$ (1,225)

[1] We record a bad debt provision based upon historical experience and a review of individual customer balances.

[2] When an individual customer balance becomes impaired and is deemed uncollectible, a deduction is made against the allowance for uncollectible accounts.

[3] We record a valuation allowance against a deferred tax asset when it is determined that it is more likely than not that the deferred tax asset will not be realized.