Investments - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
	Jul. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Equity Method Investments [Line Items]
Dividend income		$ 14,704		$ 14,879	$ 39,637	$ 45,596
Investment income and other, net
Schedule of Equity Method Investments [Line Items]
Dividend income					2,300
Income from equity method investments		3,100		$ 4,900	9,900	$ 9,300
BATS
Schedule of Equity Method Investments [Line Items]
Market value of investment in BATS		$ 398,700			398,700
Number of shares sold			2,600,000.0
Amount of equity method investment sold			$ 46,400
Ownership percentage	13.70%
BATS | Investment income and other, net
Schedule of Equity Method Investments [Line Items]
Pre-tax gain from sale of investment					$ 33,400