Summary of Significant Accounting Policies - Taxes (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Business Acquisition [Line Items]
Net income	$ 19,316,000	$ 14,170,000	$ 84,354,000	$ 21,559,000
State and local income, excise and franchise taxes	500,000	400,000	900,000	600,000
Liabilities for uncertain tax positions	0		0		$ 0
Real Estate Investment Trust
Business Acquisition [Line Items]
Net income	$ 0	$ 300,000	$ 0	$ 300,000