Condensed Consolidated Statements of Changes in Equity - 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, 2018		6,997,382	1,150,000				3,555,242
Beginning Balance at Dec. 31, 2018	$ 643,867	$ 106	$ 110,843	$ 1,209,805	$ (310,865)	$ (731)	$ (379,249)	$ 629,909	$ 13,958
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	48,443				48,672			48,672	(229)
Foreign currency translation adjustments	(2)					(2)		(2)
Net subscriptions (redemptions) and other	(802)			290				290	(1,092)
Reclassification from other comprehensive (income) loss	726					726		726
Cash dividends declared, preferred	(4,168)			(4,168)				(4,168)
Cash dividends declared, common	(8,256)			(8,256)				(8,256)
Repurchases of common shares (in shares)		(215,671)					(215,671)
Repurchases of common shares	(22,499)						$ (22,499)	(22,499)
Issuance of common shares related to employee stock transactions (in shares)		163,181
Issuance of common shares related to employee stock transactions	1,014	$ 1		1,013				1,014
Taxes paid on stock-based compensation	(6,098)			(6,098)				(6,098)
Stock-based compensation	11,447			11,447				11,447
Ending Balance (in shares) at Jun. 30, 2019		6,944,892	1,150,000				3,770,913
Ending Balance at Jun. 30, 2019	663,672	$ 107	$ 110,843	1,204,033	(262,193)	(7)	$ (401,748)	651,035	12,637
Beginning Balance at Dec. 31, 2018	57,481
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	1,924
Net subscriptions (redemptions) and other	1,097
Ending Balance at Jun. 30, 2019	60,502
Beginning Balance (in shares) at Mar. 31, 2019		6,978,925	1,150,000				3,703,204
Beginning Balance at Mar. 31, 2019	646,458	$ 107	$ 110,843	1,205,926	(289,119)	1	$ (394,248)	633,510	12,948
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	27,150				26,926			26,926	224
Foreign currency translation adjustments	(8)					(8)		(8)
Net subscriptions (redemptions) and other	(245)			290				290	(535)
Cash dividends declared, preferred	(2,084)			(2,084)				(2,084)
Cash dividends declared, common	(4,104)			(4,104)				(4,104)
Repurchases of common shares (in shares)		(67,709)					(67,709)
Repurchases of common shares	(7,500)						$ (7,500)	(7,500)
Issuance of common shares related to employee stock transactions (in shares)		33,676
Issuance of common shares related to employee stock transactions	565	$ 0		565				565
Taxes paid on stock-based compensation	(1,294)			(1,294)				(1,294)
Stock-based compensation	4,734			4,734				4,734
Ending Balance (in shares) at Jun. 30, 2019		6,944,892	1,150,000				3,770,913
Ending Balance at Jun. 30, 2019	663,672	$ 107	$ 110,843	1,204,033	(262,193)	(7)	$ (401,748)	651,035	12,637
Beginning Balance at Mar. 31, 2019	59,003
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	749
Net subscriptions (redemptions) and other	750
Ending Balance at Jun. 30, 2019	60,502
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, preferred	$ (11,676)			(11,676)				(11,676)
Repurchases of common shares (in shares)	(185,853)	(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				0
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	0				4,038,563
Beginning Balance at Mar. 31, 2020	666,466	$ 117	$ 0	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)					(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