Fair Value Measurements (Unobervable Quantitative Input Ratios) (Details) - Recurring - Level 3 - Real estate fund investments	Mar. 31, 2019	Dec. 31, 2018
Discount Rate | Minimum
Unobservable Quantitative Input
Real estate, measurement input	0.100	0.100
Discount Rate | Maximum
Unobservable Quantitative Input
Real estate, measurement input	0.150	0.150
Discount Rate | Weighted Average
Unobservable Quantitative Input
Real estate, measurement input	0.134	0.134
Cap Rate | Minimum
Unobservable Quantitative Input
Real estate, measurement input	0.055	0.054
Cap Rate | Maximum
Unobservable Quantitative Input
Real estate, measurement input	0.077	0.077
Cap Rate | Weighted Average
Unobservable Quantitative Input
Real estate, measurement input	0.058	0.057