Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands	Total	Series D convertible preferred stock	Common Stock	Preferred Stock Series D convertible preferred stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Total Attributed To Stockholders	Total Attributed To Stockholders Series D convertible preferred stock	Non- controlling Interests
Beginning Balance (in shares) at Dec. 31, 2016			5,889,013	0				3,230,045
Beginning Balance at Dec. 31, 2016	$ 321,673		$ 91	$ 0	$ 1,090,331	$ (424,279)	$ (224)	$ (344,246)	$ 321,673		$ 0
Cumulative effect adjustment for adoption of ASU at Dec. 31, 2016	1,051					1,051			1,051
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	32,587					31,514			31,514		1,073
Net unrealized gain (loss) on securities available-for-sale	172						172		172
Foreign currency translation adjustments	12						12		12
Net subscriptions (redemptions) and other	15,414										15,414
Issuance of stock, net of offering costs (in shares)			1,046,500	1,150,000
Issuance of stock, net of offering costs	109,328	$ 110,843	$ 11	$ 110,843	109,317				109,328	$ 110,843
Cash dividends declared, preferred	(6,253)				(6,253)				(6,253)
Issuance of common stock for acquisition of business (in shares)			213,669
Issuance of common stock for acquisition of business	21,740		$ 2		21,738				21,740
Cash dividends declared, common	(10,103)				(10,103)				(10,103)
Repurchases of common shares (in shares)			(66,244)					(66,244)
Repurchases of common shares	(7,502)		$ 0		0			$ (7,502)	(7,502)
Issuance of common shares related to employee stock transactions (in shares)			75,077
Issuance of common shares related to employee stock transactions	836		$ 1		835				836
Taxes paid on stock-based compensation	(3,441)				(3,441)				(3,441)
Stock-based compensation	14,317				14,317				14,317
Ending Balance (in shares) at Sep. 30, 2017			7,158,015	1,150,000				3,296,289
Ending Balance at Sep. 30, 2017	600,674		$ 105	$ 110,843	1,216,741	(391,714)	(40)	$ (351,748)	584,187		16,487
Beginning Balance at Dec. 31, 2016	37,266
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Net income (loss) attributable to noncontrolling interests	1,709
Net subscriptions (redemptions) and other	28,252
Ending Balance at Sep. 30, 2017	67,227
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
Cumulative effect adjustment for adoption of ASU at Dec. 31, 2017						(178)	178
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Acquisition of businesses	55,500
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)					(98,806)
Repurchases of common shares	$ (12,501)							$ (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]
Net income (loss) attributable to noncontrolling interests	743
Net subscriptions (redemptions) and other	(173)
Ending Balance at Sep. 30, 2018	$ 60,248