CONSOLIDATED BALANCE SHEETS [Parenthetical] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts receivable (in dollars)	$ 8,249	$ 8,071
Convertible Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible Preferred stock, shares authorized	1,000,000	1,000,000
Convertible Preferred stock, shares outstanding	0	0
Common Class A [Member]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	30,000,000	30,000,000
Common stock, shares issued	1,637,472	1,641,632
Common stock, shares outstanding	1,637,472	1,641,632
Common Class B [Member]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	2,861,843	2,861,843
Common stock, shares outstanding	2,861,843	2,861,843
Common Class C [Member]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	2,928,906	2,928,906
Common stock, shares outstanding	2,928,906	2,928,906
Common Class D [Member]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	38,845,917	41,014,121
Common stock, shares outstanding	38,845,917	41,014,121