Summary of Significant Accounting Policies - Taxes (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Business Acquisition [Line Items]
Net income	$ 24,209,000	$ 11,190,000	$ 108,563,000	$ 32,749,000
State and local income, excise and franchise taxes	400,000	300,000	1,300,000	900,000
Liabilities for uncertain tax positions	0		0		$ 0
Real Estate Investment Trust
Business Acquisition [Line Items]
Net income	$ 0	$ 0	$ 0	$ 300,000