Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts receivable	$ 844	$ 581
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
Common stock, shares, issued	20,854,739	20,854,728
Series B
Common stock, shares, issued	2,469,544	2,469,555
Treasury Stock | Series A
Treasury stock Series A, shares held	1,780,899	1,697,370