Investments - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Equity Method Investments [Line Items]
Proceeds and distributions from investments				$ 2,517	$ 48,627
Investment income and other, net	$ 4,358	$ 2,866		391,781	15,021
Investment Income and Other, Net [Member]
Schedule of Equity Method Investments [Line Items]
Income from equity method investments	$ 2,300	$ 2,100		$ 4,500	$ 15,200
BATS [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of equity in common stock of private companies cover under strategic investment	16.70%			16.70%
Percentage of voting interest held	19.90%			19.90%
BATS and DE [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds and distributions from investments			$ 42,200
Merger related transaction costs			6,600
BATS and DE [Member] | Investment Income and Other, Net [Member]
Schedule of Equity Method Investments [Line Items]
Investment income and other, net			9,600
DE [Member]
Schedule of Equity Method Investments [Line Items]
Investment income and other, net			$ 16,200