Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flows from Operating Activities:
Net income (loss)	$ 23,827	$ 13,745
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation expense, intangible asset and other amortization	6,819	960
Stock-based compensation	5,909	3,491
Amortization of deferred commissions	737	516
Payments of deferred commissions	(1,075)	(671)
Equity in earnings of equity method investments	(1,322)	(629)
Sales (purchases) of trading securities, net	4,718	2,396
Deferred taxes, net	646	2,817
Changes in operating assets and liabilities:
Accounts receivable, net and other assets	2,629	(13,013)
Accrued compensation and benefits, accounts payable, accrued liabilities and other liabilities	(51,148)	(24,305)
Operating activities of consolidated investment products (CIP):
Net cash provided by (used in) operating activities	(61,755)	(15,182)
Cash Flows from Investing Activities:
Capital expenditures	(1,275)	(369)
Purchases of available-for-sale securities	(20,302)	(66)
Net cash provided by (used in) investing activities	(21,577)	5,180
Cash Flows from Financing Activities:
Repayments on debt	(650)	(30,000)
Payment of deferred financing costs	(3,400)	(61)
Proceeds from issuance of mandatory convertible preferred stock, net of issuance costs	0	111,280
Proceeds from issuance of common stock, net of issuance costs	0	109,762
Common stock dividends paid	(3,412)	(2,894)
Preferred stock dividends paid	(2,084)	0
Stock options exercised	698	86
Taxes paid related to net share settlement of restricted stock units	(5,014)	(2,464)
Contributions (redemptions) of noncontrolling interests, net	(589)	(6,091)
Net cash provided by (used in) financing activities	(14,451)	179,191
Net increase (decrease) in cash and cash equivalents	(97,783)	169,189
Cash and cash equivalents, beginning of period	234,282	83,671
Cash and Cash Equivalent, End of Period	136,499	252,860
Non-Cash Investing Activities:
Change in accrual for capital expenditures	(375)	(166)
Non-Cash Financing Activities:
Increase (decrease) to noncontrolling interest due to consolidation (deconsolidation) of CIP, net	0	13,083
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	234,282	83,671
Consolidated entity excluding consolidated investment products
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Realized and unrealized (gains) losses on trading securities, net	(333)	(297)
Cash Flows from Financing Activities:
Cash and cash equivalents, beginning of period	132,150
Cash and Cash Equivalent, End of Period	80,764
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	132,150
Consolidated investment products
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Realized and unrealized (gains) losses on trading securities, net	(2,382)	(4,857)
Operating activities of consolidated investment products (CIP):
Purchases of investments by CIP	(264,398)	(92,478)
Sales of investments by CIP	217,564	98,191
Net purchases of short term investments by CIP	(177)	(1,735)
Sales (purchases) of securities sold short by CIP, net	190	(20)
Change in other assets of CIP	(492)	535
Change in liabilities of CIP	(3,467)	172
Cash Flows from Investing Activities:
Change in cash and cash equivalents of CIP due to consolidation, net	0	5,615
Cash Flows from Financing Activities:
Borrowings (Payments) on borrowings by CIP	0	73
Proceeds from issuance of notes payable by CIP	350,000	0
Repayment of notes payable by CIP	(350,000)	$ (500)
Cash and cash equivalents, beginning of period	101,315
Cash and Cash Equivalent, End of Period	54,836
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 101,315