Schedule III - Real Estate and Accumulated Depreciation Reconciliation of Investment Properties (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
SEC Schedule III, Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance, beginning of year	$ 939,330	$ 856,151	$ 796,008
Acquisition of new properties	607,779	0	0
Improvements	130,346	85,409	70,821
Distribution of real property to owners prior to the formation transactions	(16,345)	0	0
Disposals	(11,687)	(2,230)	(10,678)
Balance, end of year	1,649,423	939,330	856,151
Aggregate cost of investment properties for federal income tax purpose	$ 1,212,869