Schedule IV - Mortgage Loans on Real Estate (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) Unit	Dec. 31, 2017 USD ($)
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Amount December 31, 2018	$ 2,968.3	$ 3,180.5
Mortgage debt [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	2,571.2
Debt face value	2,966.5
Carrying Amount December 31, 2018	2,968.3
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Commercial [Member] | Office, 1-Month LIBOR Plus 2.25% Mortgage Payable, Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	49.5
Debt face value	49.5
Carrying Amount December 31, 2018	49.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail 4.79% Mortgage Payable Due 2018 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.79%
Balloon Amount	$ 3.5
Debt face value	3.5
Carrying Amount December 31, 2018	3.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail, 5.06% Mortgage Payable, Due 2019 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	5.06%
Balloon Amount	$ 12.3
Debt face value	12.5
Carrying Amount December 31, 2018	12.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail 4.41% Mortgage Payable Due 2018 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.41%
Balloon Amount	$ 4.9
Debt face value	4.9
Carrying Amount December 31, 2018	4.9
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Commercial [Member] | Office, Prime Plus .250% Percent Mortgage Payable, Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	16.0
Debt face value	16.0
Carrying Amount December 31, 2018	16.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail 4.68% Mortgage Payable Due 2029 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.68%
Balloon Amount	$ 27.0
Debt face value	27.0
Carrying Amount December 31, 2018	27.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail 4.10% Mortgage Payable Due 2020 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.10%
Balloon Amount	$ 10.6
Debt face value	11.0
Carrying Amount December 31, 2018	11.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail 5.75% Mortgage Payable Due 2023 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	5.75%
Balloon Amount	$ 6.2
Debt face value	7.2
Carrying Amount December 31, 2018	7.2
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail 5.00% Mortgage Payable Due 2023 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	5.00%
Balloon Amount	$ 6.0
Debt face value	6.7
Carrying Amount December 31, 2018	6.7
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail, 5.70% Mortgage Payable Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	5.70%
Balloon Amount	$ 8.1
Debt face value	10.4
Carrying Amount December 31, 2018	10.4
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail, 4.10% Mortgage Payable Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.10%
Balloon Amount	$ 6.6
Debt face value	7.3
Carrying Amount December 31, 2018	7.3
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail, 4.64% Mortgage Payable Due 2033 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.64%
Balloon Amount	$ 15.9
Debt face value	29.2
Carrying Amount December 31, 2018	29.2
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail 3.99% Mortgage Payable Due 2019 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.99%
Balloon Amount	$ 4.3
Debt face value	4.4
Carrying Amount December 31, 2018	4.4
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail, 4.20% Percent Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.20%
Balloon Amount	$ 35.0
Debt face value	35.0
Carrying Amount December 31, 2018	35.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Commercial [Member] | Office, 1-Month LIBOR Plus 2.25% Mortgage Payable, Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	27.9
Debt face value	28.8
Carrying Amount December 31, 2018	28.8
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Office, 4.20% Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.20%
Balloon Amount	$ 35.0
Debt face value	35.0
Carrying Amount December 31, 2018	35.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail, 4.75% Mortgage Payable Due 2020 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.75%
Balloon Amount	$ 7.1
Debt face value	7.4
Carrying Amount December 31, 2018	7.4
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Office, 3.85% Mortgage Payable, Due 2027 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.85%
Balloon Amount	$ 77.0
Debt face value	77.0
Carrying Amount December 31, 2018	77.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Office, 4.69% Mortgage Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.686%
Balloon Amount	$ 11.5
Debt face value	12.6
Carrying Amount December 31, 2018	12.6
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Commercial [Member] | Commercial Portflolio, 3-Month GBP LIBOR Plus1.80% Mortgage Payable, Due 2019 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	135.6
Debt face value	135.6
Carrying Amount December 31, 2018	135.6
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Retail 2.82% Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	2.82%
Balloon Amount	$ 67.7
Debt face value	67.7
Carrying Amount December 31, 2018	67.7
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Commercial [Member] | Office, 3-Month EURIBOR Plus 1.80% Mortgage Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	80.6
Debt face value	80.6
Carrying Amount December 31, 2018	80.6
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Commercial [Member] | Retail, 3-Month EURIBOR Plus 2.0% Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	90.5
Debt face value	99.7
Carrying Amount December 31, 2018	99.7
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Commercial [Member] | Office, 3-Month EURIBOR Plus 1.80% Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	78.5
Debt face value	78.5
Carrying Amount December 31, 2018	78.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Commercial Portfolio 2.90% Mortgage Payable Due 2020 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	2.90%
Balloon Amount	$ 90.1
Debt face value	90.1
Carrying Amount December 31, 2018	90.1
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Commercial Portfolio 2.91% Mortgage Payable Due 2023 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	2.91%
Balloon Amount	$ 161.7
Debt face value	206.1
Carrying Amount December 31, 2018	206.1
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Office, 2.59% Mortgage Payable Due 2024 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	2.59%
Balloon Amount	$ 83.6
Debt face value	83.6
Carrying Amount December 31, 2018	83.6
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Commercial [Member] | Retail Portfolio 3-Month EURIBOR Plus 1.60% Mortgage Payable Due 2030 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	2.4
Debt face value	41.5
Carrying Amount December 31, 2018	41.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Commercial [Member] | Retail Portfolio 3-Month EURIBOR Plus 1.60% Mortgage Payable Due 2031 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	9.8
Debt face value	48.6
Carrying Amount December 31, 2018	48.6
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Commercial [Member] | Prime Rate [Member] | Office, Prime Plus .250% Percent Mortgage Payable, Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	0.25%
Mortgage debt [Member] | Commercial [Member] | LIBOR [Member] | Office, 1-Month LIBOR Plus 2.25% Mortgage Payable, Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	2.25%
Mortgage debt [Member] | Commercial [Member] | LIBOR [Member] | Office, 1-Month LIBOR Plus 2.25% Mortgage Payable, Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	2.25%
Mortgage debt [Member] | Commercial [Member] | LIBOR [Member] | GBP [Member] | Commercial Portflolio, 3-Month GBP LIBOR Plus1.80% Mortgage Payable, Due 2019 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	1.80%
Mortgage debt [Member] | Commercial [Member] | EURIBOR [Member] | Office, 3-Month EURIBOR Plus 1.80% Mortgage Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	1.80%
Mortgage debt [Member] | Commercial [Member] | EURIBOR [Member] | Retail, 3-Month EURIBOR Plus 2.0% Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	2.00%
Mortgage debt [Member] | Commercial [Member] | EURIBOR [Member] | Office, 3-Month EURIBOR Plus 1.80% Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	1.80%
Mortgage debt [Member] | Commercial [Member] | EURIBOR [Member] | Retail Portfolio 3-Month EURIBOR Plus 1.60% Mortgage Payable Due 2030 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	1.60%
Mortgage debt [Member] | Commercial [Member] | EURIBOR [Member] | Retail Portfolio 3-Month EURIBOR Plus 1.60% Mortgage Payable Due 2031 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	1.60%
Mortgage debt [Member] | Multifamily [Member] | Multifamily 1,008 Unit 3.50% Mortgage Payable Due 2026 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.50%
Balloon Amount	$ 17.5
Debt face value	175.0
Carrying Amount December 31, 2018	175.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	1,008
Mortgage debt [Member] | Multifamily [Member] | Multifamily 460 Unit 4.07% Mortgage Payable Due 2018 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.64%
Balloon Amount	$ 46.4
Debt face value	46.7
Carrying Amount December 31, 2018	46.7
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	460
Mortgage debt [Member] | Multifamily [Member] | Multifamily 203 Unit 1-Month LIBOR Plus 1.73% Due 2026 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.86%
Balloon Amount	$ 17.7
Debt face value	19.5
Carrying Amount December 31, 2018	19.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	203
Mortgage debt [Member] | Multifamily [Member] | Multifamily 118 Unit 1-Month LIBOR Plus 1.74% Mortgage Payable Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	$ 13.5
Debt face value	13.5
Carrying Amount December 31, 2018	13.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	118
Mortgage debt [Member] | Multifamily [Member] | Multifamily 217 Unit 3.35% Mortgage Payable Due 2023 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.35%
Balloon Amount	$ 20.9
Debt face value	23.4
Carrying Amount December 31, 2018	23.4
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	217
Mortgage debt [Member] | Multifamily [Member] | Multifamily 450 Unit 3.58% Mortgage Payable Due 2023 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.58%
Balloon Amount	$ 41.5
Debt face value	46.2
Carrying Amount December 31, 2018	46.2
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	450
Mortgage debt [Member] | Multifamily [Member] | Multifamily 750 Unit 3.73% Mortgage Payable Due 2023 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.73%
Balloon Amount	$ 51.6
Debt face value	57.8
Carrying Amount December 31, 2018	58.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	750
Mortgage debt [Member] | Multifamily [Member] | Multifamily 750 Unit 1-Month LIBOR Plus 3.05% Mortgage Payable Due 2023 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	$ 25.4
Debt face value	25.4
Carrying Amount December 31, 2018	25.4
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	750
Mortgage debt [Member] | Multifamily [Member] | Multifamily 542 Unit 3.78% Mortgage Payable Due 2024 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.78%
Balloon Amount	$ 69.9
Debt face value	77.2
Carrying Amount December 31, 2018	77.2
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	542
Mortgage debt [Member] | Multifamily [Member] | Multifamily 542 Unit 1-Month LIBOR Plus 2.80% Mortgage Payable Due 2024 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	$ 0.0
Debt face value	14.3
Carrying Amount December 31, 2018	14.3
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	542
Mortgage debt [Member] | Multifamily [Member] | Multifamily 366 Unit 3.24% Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.24%
Balloon Amount	$ 47.9
Debt face value	53.3
Carrying Amount December 31, 2018	53.3
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	366
Mortgage debt [Member] | Multifamily [Member] | Multifamily 324 Unit 5.30% Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	5.30%
Balloon Amount	$ 13.8
Debt face value	15.2
Carrying Amount December 31, 2018	16.6
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	324
Mortgage debt [Member] | Multifamily [Member] | Multifamily 324 Unit 1-Month LIBOR Plus 2.64% Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	$ 8.0
Debt face value	9.0
Carrying Amount December 31, 2018	9.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	324
Mortgage debt [Member] | Multifamily [Member] | Multifamily 280 Unit 3.59% Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.59%
Balloon Amount	$ 32.9
Debt face value	37.3
Carrying Amount December 31, 2018	37.3
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	280
Mortgage debt [Member] | Multifamily [Member] | Multifamily 208 Unit 3.77% Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.77%
Balloon Amount	$ 34.1
Debt face value	37.7
Carrying Amount December 31, 2018	37.7
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	208
Mortgage debt [Member] | Multifamily [Member] | Multifamily 178 Unit Three Point Seven Four Percent Mortgage Payable Due 2027 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.74%
Balloon Amount	$ 31.4
Debt face value	31.4
Carrying Amount December 31, 2018	31.4
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	178
Mortgage debt [Member] | Multifamily [Member] | Multifamily 204 Unit Three Point Eight Nine Percent Mortgage Payable Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.89%
Balloon Amount	$ 14.3
Debt face value	14.3
Carrying Amount December 31, 2018	14.3
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	204
Mortgage debt [Member] | Multifamily [Member] | Multifamily 168 Unit 1-Month LIBOR Plus 2.36% Percent Mortgage Payable Due 2026 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.89%
Balloon Amount	$ 10.9
Debt face value	10.9
Carrying Amount December 31, 2018	10.9
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	168
Mortgage debt [Member] | Multifamily [Member] | Multifamily 430 Unit 3.63% Mortgage Payable Due 2026 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.63%
Balloon Amount	$ 56.5
Debt face value	62.6
Carrying Amount December 31, 2018	62.6
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	430
Mortgage debt [Member] | Multifamily [Member] | Multifamily 168 Unit Three Point Eight Four Percent Mortgage Payable Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.84%
Balloon Amount	$ 66.0
Debt face value	66.0
Carrying Amount December 31, 2018	66.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	386
Mortgage debt [Member] | Multifamily [Member] | Multifamily 157 Unit 3.63% Mortgage Payable Due 2026 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.63%
Balloon Amount	$ 40.6
Debt face value	42.9
Carrying Amount December 31, 2018	42.9
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	157
Mortgage debt [Member] | Multifamily [Member] | Multifamily 204 Unit 3.59% Mortgage Payable Due 2026 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.59%
Balloon Amount	$ 54.5
Debt face value	60.4
Carrying Amount December 31, 2018	60.4
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	204
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 300-Unit Building, 3.64% Mortgage Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.64%
Balloon Amount	$ 14.6
Debt face value	16.0
Carrying Amount December 31, 2018	16.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	300
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 300-Unit Building, 1-Month LIBOR Plus 3.37% Mortgage Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	$ 6.1
Debt face value	6.5
Carrying Amount December 31, 2018	6.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	300
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 210-Unit Building, 1-Month LIBOR Plus 1.52% Mortgage Payable, Due 2027 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	$ 29.0
Debt face value	29.0
Carrying Amount December 31, 2018	29.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	210
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 200-Unit Building, 4.13% Mortgage Payable, Due 2027 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.13%
Balloon Amount	$ 18.8
Debt face value	20.7
Carrying Amount December 31, 2018	20.7
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	200
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 264-Unit Building, 4.30% Mortgage Payable, Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.30%
Balloon Amount	$ 22.7
Debt face value	24.8
Carrying Amount December 31, 2018	25.4
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	264
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 343-Unit Building, 3.86% Mortgage Payable, Due 2027 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.86%
Balloon Amount	$ 84.0
Debt face value	84.0
Carrying Amount December 31, 2018	84.0
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	343
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 179-Unit Building, 3.50% Mortgage Payable, Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.50%
Balloon Amount	$ 33.3
Debt face value	33.3
Carrying Amount December 31, 2018	32.9
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	179
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 88-Unit Building, 1-Month LIBOR Plus 1.61% Mortgage Payable, Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	$ 6.2
Debt face value	8.6
Carrying Amount December 31, 2018	8.6
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	88
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 292-Unit Building, 3.88% Mortgage Payable, Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.88%
Balloon Amount	$ 57.1
Debt face value	59.1
Carrying Amount December 31, 2018	59.1
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	492
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 293-Unit Building, 4.17% Mortgage Payable, Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.17%
Balloon Amount	$ 19.9
Debt face value	19.9
Carrying Amount December 31, 2018	19.9
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	293
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 188-Unit Building, 4.33% Mortgage Payable, Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.33%
Balloon Amount	$ 12.3
Debt face value	13.5
Carrying Amount December 31, 2018	13.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	188
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 222-Unit Building, 4.28% Mortgage Payable, Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	4.275%
Balloon Amount	$ 28.8
Debt face value	28.8
Carrying Amount December 31, 2018	28.8
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	222
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 26-Unit Building, 3-Month EURIBOR Plus 1.75% Mortgage Payable, Due 2024 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	$ 10.9
Debt face value	11.8
Carrying Amount December 31, 2018	11.8
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	26
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 276-Unit Building, 2.63% Mortgage Payable, Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	2.627%
Balloon Amount	$ 81.6
Debt face value	84.2
Carrying Amount December 31, 2018	84.2
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	276
Mortgage debt [Member] | Multifamily [Member] | Multifamily, 166-Unit Building, 2.63% Percent Mortgage Payable, Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	2.627%
Balloon Amount	$ 50.3
Debt face value	51.8
Carrying Amount December 31, 2018	51.8
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Number of units | Unit	166
Mortgage debt [Member] | Multifamily [Member] | LIBOR [Member] | Multifamily 118 Unit 1-Month LIBOR Plus 1.74% Mortgage Payable Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	1.74%
Mortgage debt [Member] | Multifamily [Member] | LIBOR [Member] | Multifamily 750 Unit 1-Month LIBOR Plus 3.05% Mortgage Payable Due 2023 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	3.05%
Mortgage debt [Member] | Multifamily [Member] | LIBOR [Member] | Multifamily 542 Unit 1-Month LIBOR Plus 2.80% Mortgage Payable Due 2024 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	2.80%
Mortgage debt [Member] | Multifamily [Member] | LIBOR [Member] | Multifamily 324 Unit 1-Month LIBOR Plus 2.64% Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	2.64%
Mortgage debt [Member] | Multifamily [Member] | LIBOR [Member] | Multifamily, 300-Unit Building, 1-Month LIBOR Plus 3.37% Mortgage Payable, Due 2022 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	3.37%
Mortgage debt [Member] | Multifamily [Member] | LIBOR [Member] | Multifamily, 210-Unit Building, 1-Month LIBOR Plus 1.52% Mortgage Payable, Due 2027 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	1.52%
Mortgage debt [Member] | Multifamily [Member] | LIBOR [Member] | Multifamily, 88-Unit Building, 1-Month LIBOR Plus 1.61% Mortgage Payable, Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	1.61%
Mortgage debt [Member] | Multifamily [Member] | EURIBOR [Member] | Multifamily, 26-Unit Building, 3-Month EURIBOR Plus 1.75% Mortgage Payable, Due 2024 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	1.75%
Mortgage debt [Member] | Retail [Member] | Multifamily 168 Unit Three Point Eight Four Percent Mortgage Payable Due 2028 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of units | Unit	14
Mortgage debt [Member] | Mixed-Use And Hotel [Member] | Hotel, 5% Mortgage Payable Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	5.00%
Balloon Amount	$ 36.2
Debt face value	37.9
Carrying Amount December 31, 2018	37.9
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Mixed-Use And Hotel [Member] | Development, Mixed Use, 1-Month EURIBOR Plus 4.25% Mortgage Payable, Due 2019 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	96.5
Debt face value	96.5
Carrying Amount December 31, 2018	96.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Mixed-Use And Hotel [Member] | Hotel 3.88% Mortgage Payable Due 2025 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Interest rate (as a percent)	3.875%
Balloon Amount	$ 82.5
Debt face value	82.5
Carrying Amount December 31, 2018	82.5
Principal Amount of Loans Subject to Delinquent Principal or Interest	0.0
Mortgage debt [Member] | Mixed-Use And Hotel [Member] | Development, 1-Month LIBOR Plus 2.75% Mortgage Payable, Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Balloon Amount	0.2
Debt face value	0.2
Carrying Amount December 31, 2018	0.2
Principal Amount of Loans Subject to Delinquent Principal or Interest	$ 0.0
Mortgage debt [Member] | Mixed-Use And Hotel [Member] | LIBOR [Member] | Development, 1-Month LIBOR Plus 2.75% Mortgage Payable, Due 2021 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	2.75%
Mortgage debt [Member] | Mixed-Use And Hotel [Member] | EURIBOR [Member] | Development, Mixed Use, 1-Month EURIBOR Plus 4.25% Mortgage Payable, Due 2019 [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Basis spread on variable rate (as percent)	3.00%