Fair Value Measurements - Summary of Significant Unobservable Quantitative Inputs Utilized in Determining Fair Value of Investments (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Property Funds [Member] | Minimum [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rates	6.50%	6.50%
Terminal capitalization rates	5.50%	5.50%
Property Funds [Member] | Maximum [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rates	7.25%	7.25%
Terminal capitalization rates	6.00%	6.00%
Property Funds [Member] | Weighted average (based on fair value of investments) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rates	6.83%	6.83%
Terminal capitalization rates	5.72%	5.72%
Alternative Investment Funds [Member] | Minimum [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Preferred return	8.49%	8.50%
Alternative Investment Funds [Member] | Maximum [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Preferred return	14.00%	14.00%
Alternative Investment Funds [Member] | Weighted average (based on fair value of investments) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Preferred return	11.06%	11.07%