Consolidated Balance Sheets (unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Allowance for doubtful accounts receivable	$ 703	$ 1,055
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	125,000,000	125,000,000
Series A [Member]
Common stock, shares, issued	20,851,728	20,700,292
Series B [Member]
Common stock, shares, issued	2,469,555	2,469,755
Treasury Stock [Member] | Series A [Member]
Treasury stock Series A, shares held	1,641,925	1,430,961