Fair Value Measurements - Summary of Changes in Fair Value of Real Estate Fund Investments in Level 3 (Details) (Real Estate Fund [Member], Level 3 [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Real Estate Fund [Member] | Level 3 [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 323,387	$ 2,158,889
Purchases	22	157,687
Net unrealized gains	873	46,167
Ending Balance	$ 324,282	$ 2,362,743