Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets:
Cash and cash equivalents	$ 106,363	$ 72,277
Escrow deposits and restricted cash	39,739	59,187
Non-mortgage loans receivable, net	63,724	54,164
Debt Securities, Available-for-sale	237,360	206,442
Liabilities:
Long-term debt and short-term borrowings, gross	12,245,802	10,829,702
Redeemable OP Units, fair value	171,200	174,600
Non-Mortgage Loan Receivable
Assets:
Non-mortgage loans receivable, net	63,724	54,164
Non-mortgage loans receivable, fair value	63,538	54,081
Commercial Mortgage Backed Securities
Assets:
Debt Securities, Held-to-maturity	645,546	439,491
Debt Securities, Held-to-maturity, Fair Value	646,925	425,290
Government-Sponsored Pooled Loan Investments
Assets:
Debt Securities, Available-for-sale	59,066	56,378
Carrying Amount
Assets:
Cash and cash equivalents	106,363	72,277
Escrow deposits and restricted cash	39,739	59,187
Derivative asset	738	6,012
Liabilities:
Long-term debt and short-term borrowings, gross	12,245,802	10,829,702
Derivative Liability	12,987	4,561
Redeemable OP Units, carrying amount	171,178	174,552
Carrying Amount | Non-Mortgage Loan Receivable
Assets:
Non-mortgage loans receivable, net	63,724	54,164
Carrying Amount | Commercial Mortgage Backed Securities
Assets:
Debt Securities, Held-to-maturity	645,546	439,491
Carrying Amount | Debt Securities
Assets:
Debt Securities, Available-for-sale	237,360	206,442
Carrying Amount | Government-Sponsored Pooled Loan Investments
Assets:
Debt Securities, Available-for-sale	59,066	56,378
Fair Value
Assets:
Cash and cash equivalents, fair value	106,363	72,277
Escrow deposits and restricted cash	39,739	59,187
Derivative asset	738	6,012
Liabilities:
Long-term debt and short-term borrowings, fair value	12,778,758	10,617,074
Derivative Liability	12,987	4,561
Redeemable OP Units, fair value	171,178	174,552
Fair Value | Non-Mortgage Loan Receivable
Assets:
Non-mortgage loans receivable, fair value	63,538	54,081
Fair Value | Commercial Mortgage Backed Securities
Assets:
Debt Securities, Held-to-maturity, Fair Value	646,925	425,290
Fair Value | Debt Securities
Assets:
Debt Securities, Available-for-sale	237,360	206,442
Fair Value | Government-Sponsored Pooled Loan Investments
Assets:
Debt Securities, Available-for-sale	$ 59,066	$ 56,378