CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Common Stock Class A [Member]	Common Stock Class B [Member]	Common Stock Class C [Member]	Common Stock Class D [Member]	Additional Paid-In Capital	Accumulated Deficit [Member]
BALANCE at Dec. 31, 2017	$ 42,655	$ 0	$ 2	$ 3	$ 3	$ 41	$ 983,582	$ (940,976)
Consolidated net loss	(22,555)	0	0	0	0	0	0	(22,555)
Repurchase of common stock	(2,951)	0	0	0	0	(1)	(2,950)	0
Adjustment of redeemable noncontrolling interests to estimated redemption value	(1,202)	0	0	0	0	0	(1,202)	0
Stock-based compensation expense	1,376	0	0	0	0	1	1,375	0
BALANCE at Mar. 31, 2018	17,323	0	2	3	3	41	980,805	(963,531)
BALANCE at Dec. 31, 2018	178,700	0	2	3	3	39	978,628	(799,975)
Consolidated net loss	(6,663)	0	0	0	0	0	0	(6,663)
Repurchase of common stock	(2,448)	0	0	0	0	(1)	(2,447)	0
Exercise of options for 15,000 shares of common stock	29	0	0	0	0	0	29	0
Adjustment of redeemable noncontrolling interests to estimated redemption value	(44)	0	0	0	0	0	(44)	0
Issuance of 755,239 shares of Class D common stock	1,609	0	0	0	0	0	1,609	0
Stock-based compensation expense	511	0	0	0	0	0	511	0
BALANCE at Mar. 31, 2019	177,497	0	2	3	3	38	978,286	(800,835)
Adoption of ASC 842	$ 5,803	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 5,803