Fair Value - Transfers between Level I and Level II and Level II and Level III (Details) (USD $)	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer from level III into level II	$ 309,942,000	[1]	$ 338,294,000	[1]
Transfers from Level II into Level III	141,353,000	[1]	272,593,000	[1]
Consolidated Variable Interest Entities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Liabilities, Level 3 to Level 2 Transfers, Amount	70,300,000
Fair Value, Liabilities, Level 2 to Level 3 Transfers, Amount	$ 316,300,000

[1] Transfers between Level II and III were a result of subjecting the broker quotes on these investments to various criteria which include the number and quality of broker quotes, the standard deviation of obtained broker quotes and the percentage deviation from independent pricing services.