CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Additional Paid-In Capital	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 loss	0	(22,555)	0	0	0	0	0	(22,555)
Repurchase of common stock	(2,950)	0	0	0	0	0	(1)	(2,951)
Adjustment of redeemable noncontrolling interests to estimated redemption value	(1,202)	0	0	0	0	0	0	(1,202)
Stock-based compensation expense	1,375	0	0	0	0	0	1	1,376
BALANCE at Mar. 31, 2018	980,805	(963,531)	0	2	3	3	41	17,323
BALANCE, as of December 31, 2018	978,628	(799,975)	0	2	3	3	39	178,700
Correction of tax adjustment error - see footnote 1 (b)	0	(3,559)	0	0	0	0	0	(3,559)
BALANCE at Dec. 31, 2018	978,628	(803,534)	0	2	3	3	39	175,141
Consolidated net loss	0	(3,104)	0	0	0	0	0	(3,104)
Repurchase of common stock	(2,447)	0	0	0	0	0	(1)	(2,448)
Exercise of options for 15,000 shares of common stock	29	0	0	0	0	0	0	29
Adjustment of redeemable noncontrolling interests to estimated redemption value	(44)	0	0	0	0	0	0	(44)
Issuance of 755,239 shares of Class D common stock	1,609	0	0	0	0	0	0	1,609
Stock-based compensation expense	511	0	0	0	0	0	0	511
BALANCE at Mar. 31, 2019	978,286	(800,835)	0	2	3	3	38	177,497
Adoption of ASC 842	$ 0	$ 5,803	$ 0	$ 0	$ 0	$ 0	$ 0	$ 5,803