Summary of Significant Accounting Policies - Impact of Adoption of New Accounting Standard (Details) - USD ($) $ in Thousands	Jan. 01, 2019	Sep. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities		$ 91,356
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ground lease, initial term			50 years
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ground lease, initial term			75 years
Weighted Average Remaining Term
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ground lease, initial term			53 years 10 months 24 days
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liabilities			$ 91,700
Accounting Standards Update 2016-02 | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ground lease, initial term		40 years
Ground lease, discount rate			3.40%
Accounting Standards Update 2016-02 | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ground lease, initial term		99 years
Ground lease, discount rate			6.20%
Accounting Standards Update 2016-02 | Weighted Average Remaining Term
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Ground lease, initial term		52 years 6 months
Other Assets
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Transfers to operating lease, right-of-use assets	$ 45,000
Other liabilities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Transfers to operating lease, right-of-use assets	1,900
Accounts Payable and Accrued Liabilities
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Transfers to operating lease, right-of-use assets	$ 8,400