Schedule II Financial Information of Registrant Parent Company Balance Sheet (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets
Trading securities—at fair value	$ 3,117,429,000	$ 4,094,622,000
Cash	23,858,000	31,555,000	35,589,000	20,334,000
Restricted cash	22,527,000	24,226,000
Investment in subsidiaries, at equity in net assets	1,300,000,000
Property and equipment, at cost (less accumulated depreciation of $49,632 and $48,786)	10,516,000	7,456,000
Other assets	379,947,000	374,662,000
Total assets	5,621,691,000	5,903,200,000	6,656,765,000
LIABILITIES AND STOCKHOLDERS’ EQUITY
Long-term debt	930,072,000	663,571,000
Other liabilities	395,852,000	328,955,000
Total liabilities	4,682,046,000	5,166,875,000
Common stock: par value $.001 per share; 485,000,000 and 325,000,000 shares authorized at December 31, 2013 and December 31, 2012; 190,636,972 and 151,131,173 shares issued at December 31, 2013 and 2012, respectively; 173,099,515 and 133,647,216 shares outstanding at December 31, 2013 and 2012, respectively	191,000	151,000
Treasury stock, at cost: 17,537,457 and 17,483,957 shares at December 31, 2013 and 2012, respectively	(892,807,000)	(892,094,000)
Additional paid-in capital	2,347,104,000	1,967,414,000
Retained deficit	(552,226,000)	(355,241,000)
Accumulated other comprehensive income	37,383,000	16,095,000
Total common stockholders’ equity	939,645,000	736,325,000
Balance Sheet Parentheticals [Abstract]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	101,625,000	98,909,000
Common Stock, Par or Stated Value Per Share	$ 0.00001	$ 0.00001
Common Stock, Shares Authorized	485,000,000	325,000,000
Common Stock, Shares, Issued	190,636,972	151,131,173
Common Stock, Shares, Outstanding	173,099,515	133,647,216
Treasury Stock, Shares	17,537,457	17,483,957
Parent Company
Assets
Trading securities—at fair value	5,240,000	99,171,000
Short-term investments—at fair value	633,178,000	136,075,000
Other invested assets	0	16,666,000
Cash	4,304,000	2,978,000	453,000	1,945,000
Restricted cash	123,000	360,000
Investment in subsidiaries, at equity in net assets	1,419,360,000	1,234,229,000
Debt issuance costs	15,741,000	8,582,000
Due from affiliates, net	12,283,000	17,690,000
Property and equipment, at cost (less accumulated depreciation of $49,632 and $48,786)	1,281,000	1,344,000
Other assets	20,985,000	33,524,000
Total assets	2,112,495,000	1,550,619,000
LIABILITIES AND STOCKHOLDERS’ EQUITY
Accrued interest payable	5,551,000	3,959,000
Accrued compensation expense	132,848,000	46,835,000
Long-term debt	930,072,000	663,571,000
Federal income taxes—current and deferred	98,476,000	91,895,000
Other liabilities	5,903,000	8,034,000
Total liabilities	1,172,850,000	814,294,000
Common stock: par value $.001 per share; 485,000,000 and 325,000,000 shares authorized at December 31, 2013 and December 31, 2012; 190,636,972 and 151,131,173 shares issued at December 31, 2013 and 2012, respectively; 173,099,515 and 133,647,216 shares outstanding at December 31, 2013 and 2012, respectively	191,000	151,000
Treasury stock, at cost: 17,537,457 and 17,483,957 shares at December 31, 2013 and 2012, respectively	(892,807,000)	(892,094,000)
Additional paid-in capital	2,347,104,000	1,967,414,000
Retained deficit	(552,226,000)	(355,241,000)
Accumulated other comprehensive income	37,383,000	16,095,000
Total common stockholders’ equity	939,645,000	736,325,000
Total liabilities and stockholders’ equity	2,112,495,000	1,550,619,000
Balance Sheet Parentheticals [Abstract]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ 49,632,000	$ 48,786,000
Common Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001
Common Stock, Shares Authorized	485,000,000	325,000,000
Common Stock, Shares, Issued	190,636,972	151,131,173
Common Stock, Shares, Outstanding	173,099,515	133,647,216
Treasury Stock, Shares	17,537,457	17,483,957