CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Allowance for doubtful accounts	$ 3,720	$ 3,353
Preferred stock, par value per share (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	20,000,000	20,000,000
Preferred stock, shares issued (in shares)	3,707,256	3,707,256
Preferred stock, shares outstanding (in shares)	3,702,256	3,707,256
Treasury stock, at cost (in shares)	99,446	99,446
Class A Common Stock
Common stock, par value per share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	120,000,000	120,000,000
Common stock, shares issued (in shares)	14,478,999	14,178,284
Common stock, shares outstanding (in shares)	14,379,553	14,078,838
Class B Common Stock
Common stock, par value per share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	60,000,000	60,000,000
Common stock, shares issued (in shares)	20,800,000	20,800,000
Common stock, shares outstanding (in shares)	20,800,000	20,800,000