CONDENSED CONSOLIDATED STATEMENTS OF EQUITY UNAUDITED - USD ($) $ in Thousands	Common Stock [Member]	Retained Earnings [Member]	Additional Paid-in Capital [Member]	GBL 4% PIK Note [Member]	Accumulated Comprehensive Income [Member]	Treasury Stock [Member]	Total	Redeemable Noncontrolling Interests [Member]
Balance at Dec. 31, 2016	$ 25	$ 7,327	$ 1,007,027	$ (100,000)	$ 1,317	$ (41,674)	$ 874,022	$ 4,230
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemptions of noncontrolling interests	0	0	0	0	0	0	0	(241)
Net income (loss)	0	(13,078)	0	0	0	0	(13,078)	61
Net unrealized losses on securities available for sale, net of income tax benefit ($942)	0	0	0	0	(1,675)	0	(1,675)	0
Amounts reclassified from accumulated other comprehensive income, net of income tax expense ($6,887)	0	0	0	0	12,244	0	12,244	0
Stock based compensation expense	0	0	444	0	0	0	444	0
Proceeds from payment of GBL 4% PIK Note	0	0	0	10,000	0	0	10,000	0
Purchase of treasury stock	0	0	0	0	0	(126)	(126)	0
Balance at Mar. 31, 2017	25	(5,751)	1,007,471	(90,000)	11,886	(41,800)	881,831	4,050
Balance at Dec. 31, 2017	25	13,800	1,010,505	(50,000)	6,712	(62,895)	918,147	46,230
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassifications pursuant to adoption of new accounting guidance	0	0	6,712	0	0	(6,712)	0	0
Redemptions of noncontrolling interests	0	0	0	0	0	0	0	(1,971)
Consolidation of certain investment funds	0	0	0	0	0	0	0	6,488
Net income (loss)	0	(22,229)	0	0	0	0	(22,229)	(143)
Stock based compensation expense	0	0	72	0	0	0	72	0
Proceeds from payment of GBL 4% PIK Note	0	0	0	10,000	0	0	10,000	0
Exchange of GBL stock for AC stock	0	0	0	0	0	(17,737)	(17,737)	0
Purchase of treasury stock	0	0	0	0	0	(459)	(459)	0
Balance at Mar. 31, 2018	$ 25	$ (1,717)	$ 1,010,577	$ (40,000)	$ 0	$ (81,091)	$ 887,794	$ 50,604