Consolidated Statements of Cash Flow - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows from Operating Activities:
Net income (loss)	$ 105,508	$ 76,080	$ 39,939
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation expense, intangible asset and other amortization	39,643	33,426	18,329
Stock-based compensation	22,230	23,100	20,327
Amortization of deferred commissions	2,940	3,847	2,308
Payments of deferred commissions	(2,097)	(4,218)	(2,871)
Equity in earnings of equity method investments	(2,600)	(3,703)	(1,678)
Distributions from equity method investments	828	4,178	911
Sales (purchases) of investments, net	9,057	4,995	20,444
Other non-cash items, net	0	39	345
Deferred taxes, net	5,982	10,429	22,835
Changes in operating assets and liabilities:
Accounts receivable, net and other assets	(1,382)	24,794	(961)
Accrued compensation and benefits, accounts payable, accrued liabilities and other liabilities	(2,991)	(24,714)	11,468
Operating activities of consolidated investment products (CIP):
Net cash provided by (used in) operating activities	(36,723)	(62,555)	(182,859)
Cash Flows from Investing Activities:
Capital expenditures and other asset purchases	(7,555)	(11,717)	(1,511)
Acquisition of business, net of cash acquired	0	(126,995)	(393,446)
Sale of available-for-sale securities	2,023	37,785	0
Purchases of available-for-sale securities	0	(20,188)	(21,433)
Net cash provided by (used in) investing activities	4,448	(121,228)	(416,994)
Cash Flows from Financing Activities:
Issuance of debt	0	105,000	260,000
Payment of long term debt	(54,851)	(23,776)	(650)
Payment of contingent consideration	0	0	(51,690)
Payment of deferred financing costs	0	(3,810)	(15,549)
Borrowings (repayments) on credit facility and other debt	0	0	(30,970)
Repurchase of common shares	(40,000)	(27,501)	(7,502)
Preferred stock dividends paid	(8,338)	(8,338)	(6,253)
Common stock dividends paid	(16,977)	(14,038)	(12,581)
Proceeds from exercise of stock options	726	819	111
Taxes paid related to net share settlement of restricted stock units	(7,696)	(6,591)	(3,499)
Proceeds from issuance of mandatory convertible preferred stock, net of issuance costs	0	0	111,004
Proceeds from issuance of common stock, net of issuance costs	0	0	109,487
Net subscriptions received from (redemptions/distributions paid to) noncontrolling interests	(4,685)	(5,512)	30,047
Contributions (redemptions) of CIP	12,471	0	0
Net cash provided by (used in) financing activities	99,558	204,157	750,464
Net increase (decrease) in cash and cash equivalents	67,283	20,374	150,611
Cash, cash equivalents and restricted cash, beginning of year	254,656	234,282	83,671
Cash, cash equivalents and restricted cash, end of year	321,939	254,656	234,282
Supplemental Disclosure of Cash Flow Information
Interest paid	18,072	11,846	8,147
Income taxes paid, net	29,062	23,800	12,149
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Capital expenditures	(1,791)	2,165	70
Preferred stock dividends payable	2,084	2,084	2,084
Common stock dividends payable	4,562	3,849	965
Stock issued for acquisition of business	0	0	21,738
Accrued stock issuance costs	0	0	332
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, cash equivalents and restricted cash at end of period	321,939	234,282	234,282
Consolidated entity excluding consolidated investment products
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Realized and unrealized (gains) losses on investments of CIP, net	(6,855)	5,736	(3,237)
Consolidated investment products
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Realized and unrealized (gains) losses on investments of CIP, net	(106)	18,706	(14,051)
Operating activities of consolidated investment products (CIP):
Purchases of investments by CIP	(1,029,746)	(1,106,991)	(923,519)
Sales of investments by CIP	810,749	874,279	615,565
Net proceeds (purchases) of short term investments by CIP	4,402	(552)	595
(Purchases) sales of securities sold short by CIP, net	1,241	209	256
Change in other assets of CIP	998	(628)	(255)
Change in liabilities of CIP	971	(1,567)	5,284
Amortization of discount on notes payable of CIP	4,505	0	5,107
Cash Flows from Investing Activities:
Change in cash and cash equivalents of CIP due to consolidation (deconsolidation), net	9,980	(113)	(604)
Cash Flows from Financing Activities:
Borrowings by CIP	414,605	857,404	474,009
Payments on borrowings by CIP	(195,697)	(669,500)	(105,500)
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Increase (Decrease) to noncontrolling interests due to consolidation (deconsolidation) of CIP, net	$ (13,926)	$ 56	$ (65,576)