Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Trade receivables, related parties	$ 4,530	$ 4,653
Trade receivables, allowance for doubtful accounts	3,395	2,566
Prepaid expenses and other current assets	10,672	6,260
Property and equipment, accumulated depreciation	187,375	179,869
Accumulated amortization of Intangible assets	93,793	87,632
Intangible assets subject to amortization, net	22,598	26,758
Accounts payable and accrued expenses	51,034	61,847
Unamortized debt issuance costs	2,709	3,761
Related Parties
Prepaid expenses and other current assets	274	274
Intangible assets subject to amortization, net	8,327	9,555
Accounts payable and accrued expenses	$ 1,948	$ 2,548
Class A common stock
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	260,000,000	260,000,000
Common stock, shares issued	63,210,531	66,069,325
Common stock, shares outstanding	63,210,531	66,069,325
Class B common stock
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	40,000,000	40,000,000
Common stock, shares issued	14,927,613	14,927,613
Common stock, shares outstanding	14,927,613	14,927,613
Class U common stock
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	40,000,000	40,000,000
Common stock, shares issued	9,352,729	9,352,729
Common stock, shares outstanding	9,352,729	9,352,729