Tender Offer and Stock Repurchase - Additional Information (Details) - USD ($) $ / shares in Units, shares in Thousands		1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
	Nov. 04, 2015	Jun. 02, 2015	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	May. 04, 2015	Apr. 02, 2015	Mar. 10, 2015	Jul. 01, 2013
Class of Stock [Line Items]
Authorized repurchase amount (up to)									$ 400,000,000
Remaining authorized repurchase amount			$ 23,900,000		$ 23,900,000
Reduction in equity from retirement of repurchased shares					330,000,000
Professional fees					27,055,000	$ 25,596,000	$ 46,662,000
Repurchased amount				$ 11,324,000	$ 63,194,000	$ 111,585,000
Warrants received (in shares)			21,605		21,605	24,341
Warrants repurchased (in shares)			2,600		2,578
Warrants repurchased			$ 4,400,000
Senior Secured Notes | 6.875% Senior Secured Notes
Class of Stock [Line Items]
Interest rate			6.875%		6.875%					6.875%
GETCO
Class of Stock [Line Items]
Warrants received (in shares)											24,300
Serenity
Class of Stock [Line Items]
Repurchased amount	$ 24,500,000
Retained Earnings
Class of Stock [Line Items]
Reduction in equity from retirement of repurchased shares					$ 329,764,000
Tender Offer
Class of Stock [Line Items]
Tender offer, odd lot, percentage		29.10%
Professional fees					2,100,000
Tender Offer | Retained Earnings
Class of Stock [Line Items]
Reduction in equity from retirement of repurchased shares					$ 329,800,000
Common Class A
Class of Stock [Line Items]
Remaining authorized repurchase amount									$ 55,000,000
Repurchased shares					3,500
Repurchased amount					$ 41,700,000
Common Class A | Serenity
Class of Stock [Line Items]
Share price (in usd per share)	$ 12.89
Repurchased shares	1,900
Common Class A | Common Stock
Class of Stock [Line Items]
Reduction in equity from retirement of repurchased shares					236,000
Common Class A | Tender Offer
Class of Stock [Line Items]
Authorized repurchase amount (up to)		$ 330,000,000						$ 330,000,000
Share price (in usd per share)		$ 14.00
Common Class A | Tender Offer | Common Stock
Class of Stock [Line Items]
Reduction in equity from retirement of repurchased shares					$ 200,000
Common Class A | Tender Offer | Minimum
Class of Stock [Line Items]
Share price (in usd per share)								$ 13.50
Number of shares authorized to be repurchased		23,600
Common Class A | Tender Offer | Maximum
Class of Stock [Line Items]
Share price (in usd per share)								$ 14.00