Consolidated Statements of Cash Flow - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows from Operating Activities:
Net income (loss)	$ 76,080,000	$ 39,939,000	$ 48,763,000
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation expense, intangible asset and other amortization	33,426,000	18,329,000	5,796,000
Stock-based compensation	23,100,000	20,327,000	11,948,000
Amortization of deferred commissions	3,847,000	2,308,000	2,413,000
Payments of deferred commissions	(4,218,000)	(2,871,000)	(1,887,000)
Equity in earnings of equity method investments	(3,703,000)	(1,678,000)	(1,075,000)
Realized and unrealized (gains) losses on investments, net	5,736,000	(3,237,000)	(2,099,000)
Distributions from equity method investments	4,178,000	911,000	0
Sales (purchases) of investments, net	4,995,000	20,444,000	16,828,000
Other non-cash items, net	39,000	345,000	(3,099,000)
Deferred taxes, net	10,429,000	22,835,000	6,399,000
Changes in operating assets and liabilities:
Accounts receivable, net and other assets	24,794,000	(961,000)	(1,695,000)
Accrued compensation and benefits, accounts payable, accrued liabilities and other liabilities	(24,714,000)	11,468,000	50,000
Operating activities of consolidated investment products (CIP):
Net cash provided by (used in) operating activities	(62,555,000)	(182,859,000)	20,918,000
Cash Flows from Investing Activities:
Capital expenditures	(11,717,000)	(1,511,000)	(2,023,000)
Proceeds from sale of equity method investment	0	0	8,621,000
Equity method investment contributions	0	0	(2,471,000)
Acquisition of business, net of cash acquired	(126,995,000)	(393,446,000)	0
Sale of available-for-sale securities	37,785,000	0	0
Purchases of available-for-sale securities	(20,188,000)	(21,433,000)	(145,000)
Net cash provided by (used in) investing activities	(121,228,000)	(416,994,000)	3,079,000
Cash Flows from Financing Activities:
Issuance of debt	105,000,000	260,000,000	0
Payment of long term debt	(23,776,000)	(650,000)	0
Payment of contingent consideration	0	(51,690,000)	0
Payment of deferred financing costs	(3,810,000)	(15,549,000)	(1,159,000)
Borrowings (Repayments) on credit facility and other debt	0	(30,970,000)
Borrowings (Repayments) on credit facility and other debt			30,000,000
Repurchase of common shares	(27,501,000)	(7,502,000)	(233,757,000)
Preferred stock dividends paid	(8,338,000)	(6,253,000)	0
Common stock dividends paid	(14,038,000)	(12,581,000)	(13,774,000)
Proceeds from exercise of stock options	819,000	111,000	491,000
Taxes paid related to net share settlement of restricted stock units	(6,591,000)	(3,499,000)	(1,530,000)
Proceeds from issuance of mandatory convertible preferred stock, net of issuance costs	0	111,004,000	0
Proceeds from issuance of common stock, net of issuance costs	0	109,487,000	0
Excess tax benefits from stock-based compensation	0	0	401,000
Net subscriptions received from (redemptions/distributions paid to) noncontrolling interests	(5,512,000)
Net subscriptions received from (redemptions/distributions paid to) noncontrolling interests		30,047,000	10,904,000
Net cash provided by (used in) financing activities	204,157,000	750,464,000	(48,063,000)
Net increase (decrease) in cash and cash equivalents	20,374,000	150,611,000	(24,066,000)
Cash, cash equivalents and restricted cash, beginning of year	234,282,000	83,671,000	107,737,000
Cash, cash equivalents and restricted cash, end of year	254,656,000	234,282,000	83,671,000
Supplemental Disclosure of Cash Flow Information
Interest paid	11,846,000	8,147,000	420,000
Income taxes paid, net	23,800,000	12,149,000	16,715,000
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Capital expenditures	2,165,000	70,000	134,000
Preferred stock dividends payable	2,084,000	2,084,000	0
Common stock dividends payable	3,849,000	965,000	2,650,000
Stock issued for acquisition of business	0	21,738,000	0
Accrued stock issuance costs	0	332,000	0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash, cash equivalents and restricted cash at end of period	234,282,000	83,671,000	107,737,000
Consolidated investment products
Operating activities of consolidated investment products (CIP):
Realized and unrealized (gains) losses on investments of CIP, net	18,706,000	(14,051,000)	(3,648,000)
Purchases of investments by CIP	(1,106,991,000)	(923,519,000)	(464,216,000)
Sales of investments by CIP	874,279,000	615,565,000	400,493,000
Net proceeds (purchases) of short term investments by CIP	(552,000)	595,000	6,139,000
(Purchases) sales of securities sold short by CIP, net	209,000	256,000	(4,520,000)
Change in other assets of CIP	(628,000)	(255,000)	(1,491,000)
Change in liabilities of CIP	(1,567,000)	5,284,000	2,100,000
Amortization of discount on notes payable of CIP	0	5,107,000	3,719,000
Cash Flows from Investing Activities:
Change in cash and cash equivalents of CIP due to deconsolidation, net	(113,000)	(604,000)	(903,000)
Cash Flows from Financing Activities:
Borrowings of debt of CIP	857,404,000	0	0
(Repayment) on borrowings by CIP	(669,500,000)	(105,000,000)	(155,919,000)
Proceeds from issuance of notes payable by CIP	0	474,009,000	316,280,000
Repayment of notes payable by CIP	0	(500,000)	0
Supplemental Disclosure of Non-Cash Investing and Financing Activities
Increase (Decrease) to noncontrolling interest due to consolidation (deconsolidation) of CIP, net	$ 56,000	$ (65,576,000)	$ (47,763,000)