Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 149,987	$ 119,162
Marketable securities	15,745	27,988
Restricted cash	749	749
Trade receivables, (including related parties of $6,534 and $6,172) net of allowance for doubtful accounts of $4,757 and $3,790	132,149	142,004
Assets held for sale	6,138	2,141
Prepaid expenses and other current assets (including related parties of $274 and $274)	18,418	18,021
Total current assets	323,186	310,065
Property and equipment, net of accumulated depreciation of $192,182 and $191,183	69,737	72,004
Intangible assets subject to amortization, net of accumulated amortization of $105,578 and $103,752 (including related parties of $5,563 and $5,869)	47,587	49,412
Intangible assets not subject to amortization	211,753	216,653
Goodwill	58,043	58,043
Operating leases right of use asset	34,276	33,525
Other assets	7,586	7,643
Total assets	752,168	747,345
Current liabilities
Current maturities of long-term debt	3,000	3,000
Accounts payable and accrued expenses (including related parties of $2,042 and $2,087)	124,369	126,849
Operating lease liabilities	7,510	7,290
Total current liabilities	134,879	137,139
Long-term debt, less current maturities, net of unamortized debt issuance costs of $1,689 and $1,796	209,811	210,454
Long-term operating lease liabilities	32,015	31,775
Other long-term liabilities	3,616	3,732
Deferred income taxes	56,306	54,980
Total liabilities	436,627	438,080
Commitments and contingencies (note 6)
Redeemable noncontrolling interest	34,858	33,285
Stockholders' equity
Additional paid-in capital	827,749	828,813
Accumulated deficit	(546,357)	(551,786)
Accumulated other comprehensive income (loss)	(718)	(1,056)
Total stockholders' equity	280,683	275,980
Total liabilities and stockholders' equity	752,168	747,345
Class A common stock
Stockholders' equity
Common stock	6	6
Class B common stock
Stockholders' equity
Common stock	2	2
Class U common stock
Stockholders' equity
Common stock	$ 1	$ 1