Derivative Instruments and Hedging Activities (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative [Line Items]
Total return swap income	$ 2,270,000	$ 2,584,000
Multifamily Housing Mortgage Revenue Bonds [Member]
Derivative [Line Items]
Bond subject to interest rate caps	256,500,000
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, notional amount	$ 175,000,000
Interest rate	2.30%
Aggregate carrying value of the interest rate swap contracts, asset	$ 7,700,000		$ 5,400,000
Designated as Hedging Instrument [Member] | Interest Rate Cap [Member]
Derivative [Line Items]
Aggregate carrying value of the interest rate swap contracts, liability	0		0
Not Designated as Hedging Instrument [Member] | Total Return Swap [Member]
Derivative [Line Items]
Derivative, notional amount	9,900,000
Derivative, fair value, net	0		$ 0
Not Designated as Hedging Instrument [Member] | Total Return Swap, Callable [Member]
Derivative [Line Items]
Derivative, notional amount	$ 256,500,000