Fair Value (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) venture derivative	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Derivative instruments and Hedging Activities
Derivative, excluded component, gain, recognized in earnings		$ 753,000
Amortization period of deferred gain (loss) on discontinuation of interest rate fair value hedge	10 years
Derivative, notional amounts settled during period	$ 300,000,000
Receipts (payments) for termination of forward interest rate swaps	12,598,000	391,000	$ (14,847,000)
Gain (loss) on cash flow hedges	$ 5,132,000	$ (13,979,000)	$ (5,556,000)
Cash Flow Hedges Interest Rate Caps
Derivative instruments and Hedging Activities
Number of derivative instruments held | derivative	4
Puts
Derivative instruments and Hedging Activities
Number of ventures in which entity is required to purchase interest in investment at guaranteed minimum amount | venture	2
Interest Rate Caps | Cash Flow Hedges Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance	$ 34,155,000
Weighted average interest rate (as a percent)	4.50%
Weighted average capped interest rate (as a percent)	5.90%
Interest Rate Swap | Cash Flow Hedges Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance	$ 250,000,000
Weighted average capped interest rate (as a percent)	3.00%
Derivative, notional amounts entered into during period	$ 250,000,000
Non-designated Hedges Interest Rate Caps
Derivative instruments and Hedging Activities
Number of derivative instruments held | derivative	10
Non-designated Hedges Interest Rate Caps | Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance	$ 588,383,000
Weighted average interest rate (as a percent)	3.30%
Weighted average capped interest rate (as a percent)	6.60%
Reclassification out of Accumulated Other Comprehensive Income
Derivative instruments and Hedging Activities
Gain (loss) reclassification from accumulated OCI to income, estimated net amount to be transferred	$ 5,752,000