Significant Accounting Policies - Investments in Unconsolidated Joint Ventures/Deferred Lease Costs/Revenue Recognition/Income Taxes (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) joint_venture $ / shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares
Schedule of Equity Method Investments [Line Items]
Number of joint ventures with performance guarantees under master leases | joint_venture	1
Deferred Lease Costs [Abstract]
Portion of compensation capitalized | $	$ 6.3	$ 15.7	$ 16.4
Estimated average lease term (in years)	8 years
Days past due for income recognition on debt and preferred equity investments to be suspended	90 days
Income taxes
Federal, state and local tax provision | $	$ 1.5	$ 2.8	$ 4.3
Dividends per share paid (in dollars per share)	$ 3.40	$ 3.25	$ 3.10
Ordinary Income Dividend
Income taxes
Dividends per share paid (in dollars per share)	2.59	1.46	1.24
Capital Gains Dividend
Income taxes
Dividends per share paid (in dollars per share)	$ 0.81	$ 1.79	$ 1.86