Consolidated Statements of Cash Flow - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows from Operating Activities:
Net income (loss)	$ 39,939,000	$ 48,763,000	$ 30,671,000
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation expense, intangible asset and other amortization	18,329,000	5,796,000	6,967,000
Stock-based compensation	20,327,000	11,948,000	11,863,000
Excess tax benefit from stock-based compensation	0	(401,000)	(1,586,000)
Amortization of deferred commissions	2,308,000	2,413,000	7,924,000
Payments of deferred commissions	(2,871,000)	(1,887,000)	(3,322,000)
Equity in earnings of equity method investments	(1,678,000)	(1,075,000)	(879,000)
Realized (gain) loss on sale of equity method investment	0	(2,883,000)	0
Realized and unrealized (gains) losses on trading securities, net	(3,237,000)	(2,099,000)	1,158,000
Distributions from equity method investments	911,000	0	0
Sales (purchases) of trading securities, net	20,444,000	16,828,000	8,962,000
(Gain) loss on disposal of fixed assets	345,000	185,000	0
Deferred taxes, net	22,835,000	6,399,000	6,356,000
Changes in operating assets and liabilities:
Accounts receivable, net and other assets	(961,000)	(1,695,000)	10,620,000
Accrued compensation and benefits, accounts payable, accrued liabilities and other liabilities	11,468,000	50,000	(14,795,000)
Operating activities of consolidated investment products (CIP):
Net cash provided by (used in) operating activities	(182,692,000)	30,522,000	(209,430,000)
Cash Flows from Investing Activities:
Capital expenditures	(1,511,000)	(2,023,000)	(4,683,000)
Proceeds from sale of equity method investment	0	8,621,000	0
Equity method investment contributions	0	(2,471,000)	(1,617,000)
Acquisition of business, net of cash acquired	(393,446,000)
Acquisition of business, net of cash acquired		0	89,000
Purchases of available-for-sale securities	(21,433,000)	(145,000)	(227,000)
Net cash provided by (used in) investing activities	(416,994,000)	3,079,000	(6,438,000)
Cash Flows from Financing Activities:
Issuance of debt	260,000,000	0	0
Payment of long term debt	(650,000)	0	0
Payment of contingent consideration	(51,690,000)	0	0
Payment of deferred financing costs	(15,549,000)	(1,159,000)	(47,000)
Borrowings (Repayments) on credit facility and other debt	(30,970,000)	30,000,000	0
Repurchase of common shares	(7,502,000)	(233,757,000)	(80,000,000)
Preferred stock dividends paid	(6,253,000)	0	0
Common stock dividends paid	(12,581,000)	(13,774,000)	(16,047,000)
Proceeds from exercise of stock options	111,000	491,000	116,000
Taxes paid related to net share settlement of restricted stock units	(3,499,000)	(1,530,000)	(5,080,000)
Proceeds from issuance of mandatory convertible preferred stock, net of issuance costs	111,004,000
Proceeds from issuance of common stock, net of issuance costs	109,487,000	0	0
Excess tax benefits from stock-based compensation	0	401,000	1,586,000
Contributions of noncontrolling interests, net	30,047,000	10,904,000	55,700,000
Net cash provided by (used in) financing activities	750,464,000	(48,298,000)	109,948,000
Net increase (decrease) in cash and cash equivalents	150,778,000	(14,697,000)	(105,920,000)
Cash and cash equivalents, beginning of year	82,687,000	97,384,000	203,304,000
Cash and cash equivalents, end of year	233,465,000	82,687,000	97,384,000
Supplemental Disclosure of Cash Flow Information
Interest paid	8,147,000	420,000	266,000
Income taxes paid, net	12,149,000	16,715,000	31,850,000
Supplemental Disclosure of Non-Cash Activities
Capital expenditures	70,000	134,000	(692,000)
Preferred stock dividends payable	2,084,000	0	0
Common stock dividends payable	965,000	2,650,000	4,233,000
Stock issued for acquisition of business	21,738,000	0	0
Accrued stock issuance costs	332,000	0	0
Consolidated investment products
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Realized and unrealized (gains) losses on trading securities, net	(14,051,000)	(3,648,000)	30,037,000
Operating activities of consolidated investment products (CIP):
Purchases of investments by CIP	(923,519,000)	(464,216,000)	(653,139,000)
Sales of investments by CIP	615,565,000	400,493,000	408,416,000
Net proceeds (purchases) of short term investments by CIP	595,000	6,139,000	(54,495,000)
(Purchases) sales of securities sold short by CIP, net	256,000	(4,520,000)	(1,747,000)
Change in cash pledged or on deposit of CIP	167,000	9,604,000	(2,604,000)
Change in other assets of CIP	(255,000)	(1,491,000)	(2,428,000)
Change in liabilities of CIP	5,284,000	2,100,000	2,591,000
Amortization of discount on notes payable of CIP	5,107,000	3,719,000	0
Cash Flows from Investing Activities:
Change in cash and cash equivalents of CIP due to deconsolidation, net	(604,000)	(903,000)	0
Cash Flows from Financing Activities:
Borrowings of proceeds from short sales by CIP	0	0	1,473,000
(Repayment) Borrowings by CIP	105,000,000	156,154,000	(152,247,000)
Proceeds from issuance of notes payable by consolidated investment product	474,009,000	316,280,000	0
Repayment of notes payable by CIP	(500,000)	0	0
Cash and cash equivalents, beginning of year	18,099,000
Cash and cash equivalents, end of year	101,315,000	18,099,000
Supplemental Disclosure of Non-Cash Activities
Increase (Decrease) to noncontrolling interest due to consolidation (deconsolidation) of CIP, net	$ (65,576,000)	$ (47,763,000)	$ (648,000)