Fair Value (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended	12 Months Ended
	May 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative instruments and Hedging Activities
Notional balance			$ 215,000
Hedging losses reclassified from accumulated other comprehensive income into earnings		6,237	59,376	1,889
Charge for the reversal of the deferred loss			51,000
Estimated hedging losses to be reclassified from accumulated other comprehensive loss into earnings within the next twelve months		(5,493)
Payment for settlement of forward starting interest rate swap agreement	51,000
Cash Flow Hedges
Derivative instruments and Hedging Activities
Number of derivative instruments held		4
Amount of (decrease) increase in comprehensive loss to adjust hedging derivatives		(6,116)	(5,892)	20,987
Cash Flow Hedges | Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance		170,909
Weighted average interest rate (as a percent)		2.50%
Weighted average capped interest rate (as a percent)		5.10%
Puts
Derivative instruments and Hedging Activities
Number of ventures in which entity is required to purchase interest in investment at guaranteed minimum amount			3
Non-designated Hedges
Derivative instruments and Hedging Activities
Number of derivative instruments held		12
Non-designated Hedges | Interest Rate Caps
Derivative instruments and Hedging Activities
Notional balance		$ 605,515
Weighted average interest rate (as a percent)		1.70%
Weighted average capped interest rate (as a percent)		6.00%