Debt (Details 2) (USD $)							1 Months Ended			1 Months Ended				1 Months Ended					6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Credit Facility		Dec. 31, 2013 Credit Facility		Feb. 28, 2014 June 2014 Senior Notes	Jun. 30, 2014 June 2014 Senior Notes	Dec. 31, 2013 June 2014 Senior Notes	Feb. 28, 2014 November 2020 Senior Notes	Jun. 30, 2014 November 2020 Senior Notes	Dec. 31, 2013 November 2020 Senior Notes	Dec. 16, 2013 November 2020 Senior Notes	Feb. 28, 2014 September 2022 Senior Notes	Jun. 30, 2014 September 2022 Senior Notes	Dec. 31, 2013 September 2022 Senior Notes	Dec. 16, 2013 September 2022 Senior Notes	Mar. 31, 2014 Gross June 2014 Senior Notes	Jun. 30, 2014 Low end of the range Credit Facility	Jun. 30, 2014 High end of the range Credit Facility	Jun. 30, 2014 LIBOR Low end of the range Credit Facility	Jun. 30, 2014 LIBOR High end of the range Credit Facility	Jun. 30, 2014 Prime Low end of the range Credit Facility	Jun. 30, 2014 Prime High end of the range Credit Facility
Debt Instrument, Fair Value Disclosure [Abstract]
Credit facility			$ 1,173,175,000	[1]	$ 1,173,175,000	[1]
Credit facility	1,173,175,000	1,173,175,000
Senior notes, net	914,680,000	1,127,986,000						0	205,257,000		299,970,000	300,000,000			599,163,000	600,000,000
Senior notes, net	948,212,000	1,128,527,000
Total debt, net	2,087,855,000	2,301,161,000
Total debt, net	2,121,387,000	2,301,702,000											310,000,000				607,000,000
Line of Credit Facility, Maximum Borrowing Capacity			1,400,000,000
Credit Agreement Lender Commitment Amount			1,200,000,000
Line of Credit Facility, Remaining Borrowing Capacity	1,000,000
LineOfCreditFacilityPortionOfPropertiesRequiredToMaintainMortgages	80.00%
Debt Instrument, Basis Spread on Variable Rate																					1.50%	2.50%	0.50%	1.50%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage																			0.375%	0.50%
Debt Instrument, Face Amount											300,000,000				599,000,000			205,000,000
Debt Instrument, Interest Rate, Stated Percentage								10.25%			6.75%				6.375%
Net unamortized premiums	15,547,000	22,729,000											10,000,000				7,000,000
Extinguishment of Debt, Amount							$ 321,000			$ 30,000				$ 837,000

[1] (1) Variable interest rates of 2.66% and 2.67% at June 30, 2014, and December 31, 2013, respectively.