Investments (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments accounted for under the equity method	$ 82,476		$ 0
Common stock or equivalent of companies representing less than 20% equity ownership held at adjusted cost	41,899		48,806
Total Strategic investments	124,375		48,806
Deferred compensation investments	84		0
Knight preferred shares	0	[1]	199,632	[1]
Investment in Deephaven Funds	1,430		0
Total Investments	$ 125,889		$ 248,438
Percentage of equity in common stock of private companies cover under strategic investment	20.00%		20.00%

[1] September 30, 2013 December 31, 2012Strategic investments: Investments accounted for under the equity method$82,476 $—Common stock or equivalent of companies representing less than 20% equity ownership held at adjusted cost41,899 48,806Total Strategic investments124,375 48,806Deferred compensation investments84 —Knight preferred shares— 199,632Investment in Deephaven Funds1,430 —Total Investments$125,889 $248,438