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, 2017		7,159,645	1,150,000				3,296,289
Beginning Balance at Dec. 31, 2017	$ 605,224	$ 105	$ 110,843	$ 1,216,173	$ (386,216)	$ (600)	$ (351,748)	$ 588,557	$ 16,667
Adjustment for adoption of ASU 2016-01 at Dec. 31, 2017					(178)	178
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	74,244				73,368			73,368	876
Net unrealized gain (loss) on securities available-for-sale	(168)					(168)		(168)
Foreign currency translation adjustments	(10)					(10)		(10)
Net subscriptions (redemptions) and other	(2,036)								(2,036)
Cash dividends declared, preferred	(6,253)			(6,253)				(6,253)
Cash dividends declared, common	(11,099)			(11,099)				(11,099)
Repurchases of common shares (in shares)		98,806					98,806
Repurchases of common shares	(12,501)			0			$ (12,501)	(12,501)
Issuance of common shares related to employee stock transactions (in shares)		85,763
Issuance of common shares related to employee stock transactions	1,444			1,444				1,444
Taxes paid on stock-based compensation	(6,517)			(6,517)				(6,517)
Stock-based compensation	16,897			16,897				16,897
Ending Balance (in shares) at Sep. 30, 2018		7,146,602	1,150,000				3,395,095
Ending Balance at Sep. 30, 2018	659,225	$ 105	$ 110,843	1,210,645	(313,026)	(600)	$ (364,249)	643,718	15,507
Beginning Balance at Dec. 31, 2017	4,178
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Acquisition of business	55,500
Net income (loss) attributable to noncontrolling interests	743
Net subscriptions (redemptions) and other	(173)
Ending Balance at Sep. 30, 2018	60,248
Beginning Balance (in shares) at Jun. 30, 2018		7,166,139	1,150,000				3,356,911
Beginning Balance at Jun. 30, 2018	640,366	$ 105	$ 110,843	1,213,341	(340,024)	(622)	$ (359,248)	624,395	15,971
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	27,108				26,998			26,998	110
Net unrealized gain (loss) on securities available-for-sale	24					24		24
Foreign currency translation adjustments	(2)					(2)		(2)
Net subscriptions (redemptions) and other	(574)								(574)
Cash dividends declared, preferred	(2,085)			(2,085)				(2,085)
Cash dividends declared, common	(4,222)			(4,222)				(4,222)
Repurchases of common shares (in shares)		38,184					38,184
Repurchases of common shares	(5,001)						$ (5,001)	(5,001)
Issuance of common shares related to employee stock transactions (in shares)		18,647
Issuance of common shares related to employee stock transactions	66			66				66
Taxes paid on stock-based compensation	(1,279)			(1,279)				(1,279)
Stock-based compensation	4,824			4,824				4,824
Ending Balance (in shares) at Sep. 30, 2018		7,146,602	1,150,000				3,395,095
Ending Balance at Sep. 30, 2018	659,225	$ 105	$ 110,843	1,210,645	(313,026)	(600)	$ (364,249)	643,718	15,507
Beginning Balance at Jun. 30, 2018	3,420
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Acquisition of business	55,500
Net income (loss) attributable to noncontrolling interests	823
Net subscriptions (redemptions) and other	505
Ending Balance at Sep. 30, 2018	60,248
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)	72,460				72,757			72,757	(297)
Net unrealized gain (loss) on securities available-for-sale	0
Foreign currency translation adjustments	(14)					(14)		(14)
Net subscriptions (redemptions) and other	(911)			838				838	(1,749)
Reclassification from other comprehensive (income) loss	726					726		726
Cash dividends declared, preferred	(6,253)			(6,253)				(6,253)
Cash dividends declared, common	$ (13,228)			(13,228)				(13,228)
Repurchases of common shares (in shares)	286,620	286,620					286,620
Repurchases of common shares	$ (30,000)						$ (30,000)	(30,000)
Issuance of common shares related to employee stock transactions (in shares)		166,834
Issuance of common shares related to employee stock transactions	1,430	$ 1		1,429				1,430
Taxes paid on stock-based compensation	(6,601)			(6,601)				(6,601)
Stock-based compensation	16,140			16,140				16,140
Ending Balance (in shares) at Sep. 30, 2019		6,877,596	1,150,000				3,841,862
Ending Balance at Sep. 30, 2019	677,616	$ 107	$ 110,843	1,202,130	(238,108)	(19)	$ (409,249)	665,704	11,912
Beginning Balance at Dec. 31, 2018	57,481
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Net income (loss) attributable to noncontrolling interests	3,266
Net subscriptions (redemptions) and other	30,863
Ending Balance at Sep. 30, 2019	91,610
Beginning Balance (in shares) at Jun. 30, 2019		6,944,892	1,150,000				3,770,913
Beginning Balance at Jun. 30, 2019	663,672	$ 107	$ 110,843	1,204,033	(262,193)	(7)	$ (401,748)	651,035	12,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	24,017				24,085			24,085	(68)
Net unrealized gain (loss) on securities available-for-sale	0
Foreign currency translation adjustments	(12)					(12)		(12)
Net subscriptions (redemptions) and other	(109)			548				548	(657)
Cash dividends declared, preferred	(2,085)			(2,085)				(2,085)
Cash dividends declared, common	$ (4,972)			(4,972)				(4,972)
Repurchases of common shares (in shares)	70,949	70,949					70,949
Repurchases of common shares	$ (7,501)						$ (7,501)	(7,501)
Issuance of common shares related to employee stock transactions (in shares)		3,653
Issuance of common shares related to employee stock transactions	5	$ 0		5				5
Taxes paid on stock-based compensation	(93)			(93)				(93)
Stock-based compensation	4,694			4,694				4,694
Ending Balance (in shares) at Sep. 30, 2019		6,877,596	1,150,000				3,841,862
Ending Balance at Sep. 30, 2019	677,616	$ 107	$ 110,843	$ 1,202,130	$ (238,108)	$ (19)	$ (409,249)	$ 665,704	$ 11,912
Beginning Balance at Jun. 30, 2019	60,502
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Net income (loss) attributable to noncontrolling interests	1,342
Net subscriptions (redemptions) and other	29,766
Ending Balance at Sep. 30, 2019	$ 91,610