Derivative Instruments and Hedging Activities (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Derivative [Line Items]
Cash flow hedge ineffectiveness	$ 0	$ 0	$ 0	$ 0
Total return swap income	2,538,000	$ 3,143,000	7,653,000	$ 9,080,000
Multifamily Housing Mortgage Revenue Bonds [Member]
Derivative [Line Items]
Bond subject to interest rate caps	256,800,000		256,800,000
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, notional amount	$ 175,000,000		$ 175,000,000
Interest rate (in hundredths)	2.30%		2.30%
Aggregate carrying value of the interest rate swap contracts, asset	$ 3,800,000		$ 3,800,000		$ 4,400,000
Designated as Hedging Instrument [Member] | Interest Rate Cap [Member]
Derivative [Line Items]
Aggregate carrying value of the interest rate swap contracts, liability	0		0		0
Not Designated as Hedging Instrument [Member] | Total Return Swap [Member]
Derivative [Line Items]
Derivative, notional amount	20,700,000		20,700,000
Derivative, fair value, net	0		0		$ 0
Not Designated as Hedging Instrument [Member] | Total Return Swap, Callable [Member]
Derivative [Line Items]
Derivative, notional amount	$ 256,800,000		$ 256,800,000