Summary of Significant Accounting Policies - Recently Issued Accounting Standards (Details) $ in Thousands	Jan. 01, 2019 USD ($)	Dec. 31, 2018 lease
ASU 2016-02 | Estimated | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease assets	$ 90,000
Lease liabilities	90
ASU 2016-02 | Estimated | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease assets	110,000
Lease liabilities	$ 110
Operating ground leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating ground leases | lease		23
Corporate facility leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of operating ground leases | lease		2