Significant Accounting Policies - Additional Information (Details) $ in Thousands		3 Months Ended
	Jan. 01, 2019 USD ($)	Mar. 31, 2019 USD ($) property lease extension	Mar. 31, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest receivable		$ 3,186	$ 2,221
Common shares tendered for tax withholding		$ 344	343
Number of ground leases | lease		6
Number of properties subject to ground leases | property		5
Maximum optional ground lease extension term		70 years
Lease right-of-use assets		$ 32,242
Lease liabilities		$ 41,697
Weighted average discount rate		5.40%
Number of options to extend, more than | extension		1
Adjustment for uncollectable accounts		$ 128	52
Restatement Adjustment | Reclassification Of Earned Interest Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Interest receivable			2,200
Restatement Adjustment | Reclassification For Shares Tendered For Tax Withholding
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Common shares tendered for tax withholding			$ 300
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Term of contract		20 years
Renewal term		1 year
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Term of contract		65 years
Renewal term		15 years
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease right-of-use assets	$ 32,200
Lease liabilities	$ 41,400
Weighted average discount rate	5.40%
Adjustment for uncollectable accounts	$ 200