Summary of Significant Accounting Policies (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended	1 Months Ended	12 Months Ended		1 Months Ended	3 Months Ended
	Dec. 31, 2014	Aug. 31, 2009	Dec. 31, 2013	Dec. 31, 2012	Aug. 31, 2012	Dec. 31, 2014	Jul. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	May 31, 2014
DEFERRED FINANCING FEES
Issuance costs capitalized	$ 8,039		$ 3,326	$ 12,608		$ 8,039
Principal amount of debt	1,750,000		1,100,000			1,750,000
Unamortized gross balance of deferred financing fees	50,479		19,930			50,479
Accumulated amortization related to deferred financing fees	42,797		14,822			42,797
Weighted average amortization period of deferred financing fees	12 years 8 months 12 days
Amortization of deferred financing fees
Amortization expense in 2015	5,469
Amortization expense in 2016	4,803
Amortization expense in 2017	4,523
Amortization expense in 2018	3,127
Amortization expense in 2019	2,389
Amortization expense thereafter	10,238
Senior unsecured notes 6.75%
DEFERRED FINANCING FEES
Issuance costs capitalized							11,439	44
Principal amount of debt	200,000		200,000			200,000	350,000	300,000
Mortgage financing closed in August 2009
DEFERRED FINANCING FEES
Principal amount of debt		512,934
Early repayment of debt variable portion		199,197
Previous unsecured revolving credit facility
DEFERRED FINANCING FEES
Deferred financing fees and unamortized discounts written off	357		538	3,897
Unsecured revolving credit facility
DEFERRED FINANCING FEES
Issuance costs capitalized									3,078
Mortgages
DEFERRED FINANCING FEES
Issuance costs capitalized			248	1,125						199
Early repayment of debt variable portion					199,197	23,234
Senior notes issued in April 2014
DEFERRED FINANCING FEES
Issuance costs capitalized	5,021					5,021
Number of senior notes issued	2					2
Unsecured Debt
DEFERRED FINANCING FEES
Issuance costs capitalized										2,819
Principal amount of debt	$ 350,000					$ 350,000				$ 350,000