Real Estate Investments - Allocation of Assets Acquired (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 property	Dec. 31, 2012 property	Dec. 31, 2011
Real Estate Properties [Line Items]
Land	$ 301,167	$ 223,917
Buildings, fixtures and improvements	948,048	1,174,747
Total tangible assets	1,249,215	1,398,664
Total assets acquired, net	1,381,278	1,589,110
Below market leases	(4,200)	0
Total liabilities acquired, net	(4,200)	0
OP units issued to acquire real estate investment	0	(6,352)	0
Cash paid for acquired real estate investments	1,377,078	1,582,758	89,981
Number of properties acquired	569	524
Leases, Acquired-in-Place [Member]
Real Estate Properties [Line Items]
Acquired intangible assets:	132,063	189,182
Above Market Leases [Member]
Real Estate Properties [Line Items]
Acquired intangible assets:	$ 0	$ 1,264