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
Valuation and Qualifying Accounts
Balance at Beginning of Year	$ 1,675	$ 1,526	$ 1,328
Additions Charged to Costs and Expenses	2,926	1,402	1,426
Deductions Returns and Write-Offs	(3,185)	(1,253)	(1,228)
Balance at End of Year	1,416	1,675	1,526
Income tax valuation allowance
Valuation and Qualifying Accounts
Balance at Beginning of Year	2,682	2,576	988
Additions Charged to Costs and Expenses	153	183
Charged to Other Accounts	(325)		1,616
Deductions Returns and Write-Offs		(77)	(28)
Balance at End of Year	$ 2,510	$ 2,682	$ 2,576