Investments - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Dec. 31, 2016	Nov. 30, 2016	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Mar. 10, 2015
Schedule of Equity Method Investments [Line Items]
Dividend income			$ 10,360		$ 11,921
Warrants received (in shares)	6,182,000		4,472,000	6,182,000
Investments held at fair value	$ 9,198		$ 2,379	$ 9,198
Investment income and other, net
Schedule of Equity Method Investments [Line Items]
Income from equity method investments			48		4,800
Dividend income					$ 2,300
BATS
Schedule of Equity Method Investments [Line Items]
Number of shares sold		13,000,000
Remaining shares owned	206,000			206,000
Ownership percentage	0.50%
Investments held at fair value	$ 6,900			$ 6,900
Pre-tax gain from sale of investment			$ 4,800
Open Market Transactions | BATS
Schedule of Equity Method Investments [Line Items]
Number of shares sold				2,000,000
Block Sale | BATS
Schedule of Equity Method Investments [Line Items]
Number of shares sold				2,200,000.0
Swap Transaction
Schedule of Equity Method Investments [Line Items]
Warrants received (in shares)		8,100,000
Warrants retained (in shares)		1,100,000
Portion of transaction costs (in shares)		46,000
Swap Transaction | BATS
Schedule of Equity Method Investments [Line Items]
Number of shares exchanged in transaction		8,900,000
Number of shares retained in transaction	94,000			94,000
Receivable included in other assets	$ 2,900			$ 2,900
Liability included in accrued expenses and other liabilities	$ 2,900			$ 2,900
Fair value of portion of transaction costs		$ 1,400
Number of shares treated as derivatives	48,000			48,000
General Atlantic | Common Class A | Swap Transaction
Schedule of Equity Method Investments [Line Items]
Number of shares exchanged in transaction		18,700,000
Senior Secured Notes | 6.875% Senior Secured Notes
Schedule of Equity Method Investments [Line Items]
Interest rate (percent)	6.875%		6.875%	6.875%	6.875%	6.875%
Jefferies LLC | Swap Transaction
Schedule of Equity Method Investments [Line Items]
Payments of stock issuance costs		$ 2,900