Unconsolidated real estate joint ventures (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments
Investment in unconsolidated real estate joint ventures	$ 346,890	$ 237,507
Unconsolidated Real Estate Joint Venture Debt
Weighted Average Interest Rate at End of Period	3.91%
Long-term Debt	$ 6,777,479
Equity Method Investee
Unconsolidated Real Estate Joint Venture Debt
Long-term Debt	543,027
Long-term debt, remaining commitments	173,582
Menlo Gateway \| Equity Method Investee
Schedule of Equity Method Investments
Investment in unconsolidated real estate joint ventures	$ 288,408	186,504
Equity interest percentage (in percent)	49.00%
Menlo Gateway \| Equity Method Investee \| Secured debt maturing on 5/1/35
Unconsolidated Real Estate Joint Venture Debt
Maturity date	May 01, 2035
Stated interest rate (as a percent)	4.53%
Weighted Average Interest Rate at End of Period	4.59%
Long-term Debt	$ 56,321
Long-term Debt, Percentage Bearing Fixed Interest, Remaining Commitments	$ 99,529
Menlo Gateway \| Equity Method Investee \| Secured debt maturing on 8/1/35
Unconsolidated Real Estate Joint Venture Debt
Maturity date	Aug. 10, 2035
Stated interest rate (as a percent)	4.15%
Weighted Average Interest Rate at End of Period	4.18%
Long-term Debt	$ 142,101
Long-term Debt, Percentage Bearing Fixed Interest, Remaining Commitments	0
1401/1413 Research Boulevard \| Equity Method Investee
Schedule of Equity Method Investments
Investment in unconsolidated real estate joint ventures	$ 7,696	8,197
Equity interest percentage (in percent)	65.00%
1401/1413 Research Boulevard \| Equity Method Investee \| Secured debt maturing on 5/17/20
Unconsolidated Real Estate Joint Venture Debt
Maturity date	May 17, 2020
Weighted Average Interest Rate at End of Period	5.18%
Long-term Debt	$ 26,158
Long-term Debt, Percentage Bearing Variable Interest, Remaining Commitments	$ 2,619
1401/1413 Research Boulevard \| Equity Method Investee \| Secured debt maturing on 5/17/20 \| LIBOR
Unconsolidated Real Estate Joint Venture Debt
Applicable margin (as a percent)	2.50%
704 Quince Orchard Road \| Equity Method Investee
Schedule of Equity Method Investments
Investment in unconsolidated real estate joint ventures	$ 4,748	4,547
Equity interest percentage (in percent)	56.80%
704 Quince Orchard Road \| Equity Method Investee \| Secured debt maturing on 3/16/23
Unconsolidated Real Estate Joint Venture Debt
Maturity date	Mar. 16, 2023
Weighted Average Interest Rate at End of Period	3.94%
Long-term Debt	$ 9,172
Long-term Debt, Percentage Bearing Variable Interest, Remaining Commitments	$ 5,709
704 Quince Orchard Road \| Equity Method Investee \| Secured debt maturing on 3/16/23 \| LIBOR
Unconsolidated Real Estate Joint Venture Debt
Applicable margin (as a percent)	1.95%
1655 and 1715 Third Street \| Equity Method Investee
Schedule of Equity Method Investments
Investment in unconsolidated real estate joint ventures	$ 37,016	34,917
Equity interest percentage (in percent)	10.00%
1655 and 1715 Third Street \| Equity Method Investee \| Secured debt maturing on 6/29/21
Unconsolidated Real Estate Joint Venture Debt
Maturity date	Jun. 29, 2021
Weighted Average Interest Rate at End of Period	5.41%
Long-term Debt	$ 309,275
Long-term Debt, Percentage Bearing Variable Interest, Remaining Commitments	$ 65,725
1655 and 1715 Third Street \| Equity Method Investee \| Secured debt maturing on 6/29/21 \| LIBOR
Unconsolidated Real Estate Joint Venture Debt
Applicable margin (as a percent)	3.70%
Other unconsolidated real estate joint ventures \| Equity Method Investee
Schedule of Equity Method Investments
Investment in unconsolidated real estate joint ventures	$ 9,022	$ 3,342

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