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 (As Revised) at Dec. 31, 2017	$ 983,582	$ (940,976)	$ 0	$ 2	$ 3	$ 3	$ 41	$ 42,655
Consolidated net income	0	24,079	0	0	0	0	0	24,079
Repurchase of common stock	(6,127)	0	0	0	0	0	(3)	(6,130)
Repurchase of share-based equity awards	(1,077)	0	0	0	0	0	0	(1,077)
Exercise of options for 15,000 and 58,190 shares of common stock	85	0	0	0	0	0	0	85
Adjustment of redeemable noncontrolling interests to estimated redemption value	(463)	0	0	0	0	0	0	(463)
Stock-based compensation expense	3,633	0	0	0	0	0	2	3,635
BALANCE at Sep. 30, 2018	979,633	(916,897)	0	2	3	3	40	62,784
BALANCE	978,628	(799,975)	0	2	3	3	39	178,700
Correction of tax adjustment	0	(3,559)	0	0	0	0	0	(3,559)
BALANCE (As Revised) at Dec. 31, 2018	978,628	(803,534)	0	2	3	3	39	175,141
Consolidated net income	0	8,846	0	0	0	0	0	8,846
Repurchase of common stock	(5,321)	0	0	0	0	0	(2)	(5,323)
Exercise of options for 15,000 and 58,190 shares of common stock	29	0	0	0	0	0	0	29
Adjustment of redeemable noncontrolling interests to estimated redemption value	984	0	0	0	0	0	0	984
Issuance of 755,239 shares of Class D common stock	1,609	0	0	0	0	0	0	1,609
Stock-based compensation expense	2,590	0	0	0	0	0	2	2,592
BALANCE at Sep. 30, 2019	978,519	(788,885)	0	2	3	3	39	189,681
Adoption of ASC 842	$ 0	$ 5,803	$ 0	$ 0	$ 0	$ 0	$ 0	$ 5,803