Sale of BondPoint - Summary of Carrying Value and Gain on Sale (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 02, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business assets and liabilities held for sale:
Gain on sale of BondPoint, net of transaction costs		$ 0	$ 335,211	$ 0
BondPoint
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total sale proceeds received		$ 0	400,192	0
BondPoint | Held for Sale
Business assets and liabilities held for sale:
Receivables from broker dealers and clearing organizations				3,383
Intangibles and other assets				51,687
Liabilities				(728)
Total carrying value of BondPoint				54,342
BondPoint | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total sale proceeds received	$ 400,192
Business assets and liabilities held for sale:
Goodwill adjustment allocated to BondPoint	8,300
Gain on sale of BondPoint	337,550		$ 337,600	$ 86,600
Transaction costs	8,568
Gain on sale of BondPoint, net of transaction costs	$ 328,982