Real Estate Investments - Schedule of Acquisitions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2014	Jun. 30, 2014	Sep. 30, 2014	Dec. 31, 2014 property	Dec. 31, 2013 property	Dec. 31, 2012 property
Real estate investments, at cost:
Land				$ 288,376	$ 44,118	$ 519
Buildings, fixtures and improvements				1,450,862	103,127	1,210
Total tangible assets				1,739,238	147,245	1,729
Intangibles acquired:
Goodwill				3,665	0	0
Total assets acquired, net				2,171,421	188,286	2,585
Mortgage notes payable used to acquire real estate investments				(217,791)	(75,651)	(1,228)
Credit facility borrowings used to acquire real estate investments	(36,265)	(71,528)	(309,096)	(446,558)	0	0
Other liabilities assumed				0	(1,664)	0
Cash paid for acquired real estate investments				1,507,072	110,971	1,357
Number of properties purchased				270	36	1
Leases, Acquired-in-Place
Intangibles acquired:
Assets Acquired				418,419	44,865	647
Above Market Leases
Intangibles acquired:
Assets Acquired				26,711	2,159	209
Below Market Lease
Intangibles acquired:
Assets Acquired				(17,513)	(5,983)	0
Below Market Ground Lease
Intangibles acquired:
Assets Acquired				$ 901	$ 0	$ 0