Fair Value (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) derivative	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) derivative	Jun. 30, 2015 USD ($)
Derivative instruments and Hedging Activities
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	$ (26,788,000)	$ (6,000)	$ (74,545,000)	$ (36,000)
Payments for Hedge, Financing Activities			14,847,000	$ 0
Estimated hedging losses to be reclassified from accumulated other comprehensive loss into earnings within the next twelve months			$ 6,978,000
Cash Flow Hedges
Derivative instruments and Hedging Activities
Number of derivative instruments held | derivative	11		11
Interest Rate Cap [Member] | Cash Flow Hedges
Derivative instruments and Hedging Activities
Notional amount	$ 36,317,000		$ 36,317,000
Weighted average interest rate (as a percent)	2.60%		2.60%
Weighted average capped interest rate (as a percent)	5.90%		5.90%
Interest Rate Swap [Member] | Cash Flow Hedges
Derivative instruments and Hedging Activities
Notional amount	$ 800,000,000		$ 800,000,000
Notional amounts entered into during period	150,000,000		$ 600,000,000
Derivative, Notional Amounts Settled During Period	$ 400,000,000
Weighted average capped interest rate (as a percent)	2.30%		2.30%
Not Designated as Hedging Instrument [Member]
Derivative instruments and Hedging Activities
Number of derivative instruments held | derivative	15		15
Not Designated as Hedging Instrument [Member] | Interest Rate Cap [Member]
Derivative instruments and Hedging Activities
Notional amount	$ 723,831,000		$ 723,831,000
Weighted average interest rate (as a percent)	2.20%		2.20%
Weighted average capped interest rate (as a percent)	6.20%		6.20%