Schedule II - Valuation and Qualifying Accounts (Valuation and Qualifying Accounts) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Sales returns and allowances [Member]
Valuation and Qualifying Accounts
Balance at beginning of period		$ 7,978	$ 6,855	$ 6,500
Additions - charged to costs and expenses		1,617	1,123	355
Additions - charged to other accounts - describe		0	0	0
Deductions - describe		0	0	0
Balance at end of period		9,595	7,978	6,855
Allowance for doubtful accounts [Member]
Valuation and Qualifying Accounts
Balance at beginning of period		9,637	8,713	6,661
Additions - charged to costs and expenses		9,587	7,119	8,919
Additions - charged to other accounts - describe		0	0	0
Deductions - describe	[1]	7,184	6,195	6,867
Balance at end of period		$ 12,040	$ 9,637	$ 8,713

[1] Uncollectable accounts written off.