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)	47,136				46,370			46,370	766
Net unrealized gain (loss) on securities available-for-sale	(192)					(192)		(192)
Foreign currency translation adjustments	(8)					(8)		(8)
Net subscriptions (redemptions) and other	(1,462)								(1,462)
Cash dividends declared, preferred	(4,168)			(4,168)				(4,168)
Cash dividends declared, common	(6,877)			(6,877)				(6,877)
Repurchases of common shares (in shares)		(60,622)					(60,622)
Repurchases of common shares	(7,500)			0			$ (7,500)	(7,500)
Issuance of common shares related to employee stock transactions (in shares)		67,116
Issuance of common shares related to employee stock transactions	1,378			1,378				1,378
Taxes paid on stock-based compensation	(5,238)			(5,238)				(5,238)
Stock-based compensation	12,073			12,073				12,073
Ending Balance (in shares) at Jun. 30, 2018		7,166,139	1,150,000				3,356,911
Ending Balance at Jun. 30, 2018	640,366	$ 105	$ 110,843	1,213,341	(340,024)	(622)	$ (359,248)	624,395	15,971
Beginning Balance at Dec. 31, 2017	4,178
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Net income (loss) attributable to noncontrolling interests	(80)
Net subscriptions (redemptions) and other	(678)
Ending Balance at Jun. 30, 2018	3,420
Beginning Balance (in shares) at Mar. 31, 2018		7,217,443	1,150,000				3,296,289
Beginning Balance at Mar. 31, 2018	625,406	$ 105	$ 110,843	1,213,342	(363,094)	(661)	$ (351,748)	608,787	16,619
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	23,164				23,070			23,070	94
Net unrealized gain (loss) on securities available-for-sale	57					57		57
Foreign currency translation adjustments	(18)					(18)		(18)
Net subscriptions (redemptions) and other	(742)								(742)
Cash dividends declared, preferred	(2,084)			(2,084)				(2,084)
Cash dividends declared, common	(3,483)			(3,483)				(3,483)
Repurchases of common shares (in shares)		(60,622)					(60,622)
Repurchases of common shares	(7,500)						$ (7,500)	(7,500)
Issuance of common shares related to employee stock transactions (in shares)		9,318
Issuance of common shares related to employee stock transactions	680			680				680
Taxes paid on stock-based compensation	(224)			(224)				(224)
Stock-based compensation	5,110			5,110				5,110
Ending Balance (in shares) at Jun. 30, 2018		7,166,139	1,150,000				3,356,911
Ending Balance at Jun. 30, 2018	640,366	$ 105	$ 110,843	1,213,341	(340,024)	(622)	$ (359,248)	624,395	15,971
Beginning Balance at Mar. 31, 2018	4,162
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Net income (loss) attributable to noncontrolling interests	65
Net subscriptions (redemptions) and other	(807)
Ending Balance at Jun. 30, 2018	3,420
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)
Net unrealized gain (loss) on securities available-for-sale	0
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)					(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]
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
Net unrealized gain (loss) on securities available-for-sale	0
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)					(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]
Net income (loss) attributable to noncontrolling interests	749
Net subscriptions (redemptions) and other	750
Ending Balance at Jun. 30, 2019	$ 60,502