Fair Value Measurements (Narratives) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) Investments	Dec. 31, 2016 USD ($)
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Real estate fund investments	$ 455,692	$ 462,132
Real estate fund investments
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Number Of Investments Held By Fund | Investments	6
Real estate fund investments	$ 455,692
Excess of fair value over cost	143,092
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Real estate fund investments	455,692	462,132
Recurring | Level 3
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Real estate fund investments	455,692	$ 462,132
Excess of fair value over cost	$ 143,092
Recurring | Level 3 | Real estate fund investments | Minimum
Fair Value Inputs [Abstract]
Anticipated holding period of investments	4 months
Recurring | Level 3 | Real estate fund investments | Maximum
Fair Value Inputs [Abstract]
Anticipated holding period of investments	3 years 6 months