CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Convertible Preferred Stock [Member]	Common Stock Class A [Member]	Common Stock Class B [Member]	Common Stock Class C [Member]	Common Stock Class D [Member]	Total
BALANCE at Dec. 31, 2017	$ 983,582	$ (940,976)	$ 0	$ 2	$ 3	$ 3	$ 41	$ 42,655
Consolidated net income	0	137,442	0	0	0	0	0	137,442
Repurchase of common stock	(8,164)	0	0	0	0	0	(4)	(8,168)
Repurchase of share-based equity awards	(1,077)	0	0	0	0	0	0	(1,077)
Exercise of options for common stock	94	0	0	0	0	0	0	94
Adjustment of redeemable noncontrolling interests to estimated redemption value	(516)	0	0	0	0	0	0	(516)
Stock-based compensation expense	4,709	0	0	0	0	0	2	4,711
BALANCE at Dec. 31, 2018	978,628	(803,534)	0	2	3	3	39	175,141
Consolidated net income	0	925	0	0	0	0	0	925
Repurchase of common stock	(5,513)	0	0	0	0	0	(2)	(5,515)
Exercise of options for common stock	29	0	0	0	0	0	0	29
Adjustment of redeemable noncontrolling interests to estimated redemption value	(200)	0	0	0	0	0	0	(200)
Issuance of 978,844 shares of Class D common stock	2,108	0	0	0	0	0	0	2,108
Stock-based compensation expense	4,782	0	0	0	0	0	2	4,784
BALANCE at Dec. 31, 2019	979,834	(796,806)	0	2	3	3	39	183,075
Adoption of ASC 842	$ 0	$ 5,803	$ 0	$ 0	$ 0	$ 0	$ 0	$ 5,803