Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 52,003	$ 46,733
Marketable securities	122,570	132,424
Restricted cash	732	732
Trade receivables, (including related parties of $4,752 and $4,530) net of allowance for doubtful accounts of $3,285 and $3,395	65,745	79,308
Assets held for sale	1,179	1,179
Prepaid expenses and other current assets (including related parties of $274 and $274)	12,006	10,672
Total current assets	254,235	271,048
Property and equipment, net of accumulated depreciation of $185,138 and $187,375	69,455	64,939
Intangible assets subject to amortization, net of accumulated amortization of $95,475 and $93,793 (including related parties of $8,245 and $8,327)	20,916	22,598
Intangible assets not subject to amortization	254,598	254,598
Goodwill	74,225	74,292
Operating leases right of use asset	44,070
Other assets	2,689	2,934
Total assets	720,188	690,409
Current liabilities
Current maturities of long-term debt	3,000	3,000
Accounts payable and accrued expenses (including related parties of $2,102 and $1,948)	44,853	51,034
Operating lease liabilities	10,599
Total current liabilities	58,452	54,034
Long-term debt, less current maturities, net of unamortized debt issuance costs of $2,611 and $2,709	239,889	240,541
Long-term operating lease liabilities	40,099
Other long-term liabilities	10,383	16,418
Deferred income taxes	47,635	46,684
Total liabilities	396,458	357,677
Commitments and contingencies (note 5)
Stockholders' equity
Additional paid-in capital	851,080	862,299
Accumulated deficit	(526,740)	(528,164)
Accumulated other comprehensive income (loss)	(619)	(1,412)
Total stockholders' equity	323,730	332,732
Total liabilities and stockholders' equity	720,188	690,409
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