Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Preferred Stock Series D convertible preferred stock	Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Total Attributed To Stockholders	Non- controlling Interests
Beginning Balance (in shares) at Dec. 31, 2019		6,809,280	1,150,000				3,927,607
Beginning Balance at Dec. 31, 2019	$ 686,257	$ 107	$ 110,843	$ 1,199,205	$ (215,216)	$ 9	$ (419,249)	$ 675,699	$ 10,558
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	5,871				6,994			6,994	(1,123)
Foreign currency translation adjustments	(26)					(26)		(26)
Net subscriptions (redemptions) and other	(1,257)			(167)				(167)	(1,090)
Cash dividends declared, common	(11,676)			(11,676)				(11,676)
Repurchases of common shares (in shares)		(185,853)					185,853
Repurchases of common shares	(17,500)						$ (17,500)	(17,500)
Conversion of preferred stock (in shares)		912,806	(1,150,000)
Conversion of preferred stock	0	$ 9	$ (110,843)	110,834
Issuance of common shares related to employee stock transactions (in shares)		128,039
Issuance of common shares related to employee stock transactions	114	$ 2		112				114
Taxes paid on stock-based compensation	(5,569)			(5,569)				(5,569)
Stock-based compensation	10,297			10,297				10,297
Ending Balance (in shares) at Jun. 30, 2020		7,664,272	0				4,113,460
Ending Balance at Jun. 30, 2020	666,511	$ 118	$ 0	1,303,036	(208,222)	(17)	$ (436,749)	658,166	8,345
Beginning Balance at Dec. 31, 2019	63,845
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	11,344
Net subscriptions (redemptions) and other	15,498
Ending Balance at Jun. 30, 2020	90,687
Beginning Balance (in shares) at Mar. 31, 2020		7,695,413					4,038,563
Beginning Balance at Mar. 31, 2020	666,466	$ 117		1,304,868	(219,501)	(16)	$ (429,249)	656,219	10,247
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	9,901				11,279			11,279	(1,378)
Foreign currency translation adjustments	(1)					(1)		(1)
Net subscriptions (redemptions) and other	(691)			(167)				(167)	(524)
Cash dividends declared, common	(5,496)			(5,496)				(5,496)
Repurchases of common shares (in shares)		(74,897)					74,897
Repurchases of common shares	(7,500)						$ (7,500)	(7,500)
Issuance of common shares related to employee stock transactions (in shares)		43,756
Issuance of common shares related to employee stock transactions	13	$ 1		12				13
Taxes paid on stock-based compensation	(2,019)			(2,019)				(2,019)
Stock-based compensation	5,838			5,838				5,838
Ending Balance (in shares) at Jun. 30, 2020		7,664,272	0				4,113,460
Ending Balance at Jun. 30, 2020	666,511	$ 118	$ 0	1,303,036	(208,222)	(17)	$ (436,749)	658,166	8,345
Beginning Balance at Mar. 31, 2020	87,115
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	6,308
Net subscriptions (redemptions) and other	(2,736)
Ending Balance at Jun. 30, 2020	90,687
Beginning Balance (in shares) at Dec. 31, 2020		7,583,466	0				4,207,403
Beginning Balance at Dec. 31, 2020	720,940	$ 118	$ 0	1,298,002	(135,259)	29	$ (451,749)	711,141	9,799
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	99,900				99,555			99,555	345
Foreign currency translation adjustments	6					6		6
Net subscriptions (redemptions) and other	$ (1,176)								(1,176)
Repurchases of common shares (in shares)	(46,833)	(46,833)					46,833
Repurchases of common shares	$ (12,499)						$ (12,499)	(12,499)
Cash dividends declared, preferred	(13,300)			(13,300)				(13,300)
Issuance of common shares related to employee stock transactions (in shares)		114,973
Issuance of common shares related to employee stock transactions	66	$ 1		65				66
Taxes paid on stock-based compensation	(19,280)			(19,280)				(19,280)
Stock-based compensation	15,180			15,180				15,180
Ending Balance (in shares) at Jun. 30, 2021		7,651,606	0				4,254,236
Ending Balance at Jun. 30, 2021	789,837	$ 119	$ 0	1,280,667	(35,704)	35	$ (464,248)	780,869	8,968
Beginning Balance at Dec. 31, 2020	115,513
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	28,411
Net subscriptions (redemptions) and other	(12,399)
Ending Balance at Jun. 30, 2021	131,525
Beginning Balance (in shares) at Mar. 31, 2021		7,649,679					4,227,315
Beginning Balance at Mar. 31, 2021	738,695	$ 119		1,284,643	(98,671)	35	$ (456,748)	729,378	9,317
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	63,237				62,967			62,967	270
Foreign currency translation adjustments	0					0		0
Net subscriptions (redemptions) and other	(619)								(619)
Cash dividends declared, common	$ (6,604)			(6,604)				(6,604)
Repurchases of common shares (in shares)	(26,921)	(26,921)					26,921
Repurchases of common shares	$ (7,500)						$ (7,500)	(7,500)
Issuance of common shares related to employee stock transactions (in shares)		28,848
Taxes paid on stock-based compensation	(4,117)			(4,117)				(4,117)
Stock-based compensation	6,745			6,745				6,745
Ending Balance (in shares) at Jun. 30, 2021		7,651,606	0				4,254,236
Ending Balance at Jun. 30, 2021	789,837	$ 119	$ 0	$ 1,280,667	$ (35,704)	$ 35	$ (464,248)	$ 780,869	$ 8,968
Beginning Balance at Mar. 31, 2021	112,482
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	12,860
Net subscriptions (redemptions) and other	6,183
Ending Balance at Jun. 30, 2021	$ 131,525