Mergers with Real Estate Businesses (CapLease, Inc. Merger) (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Nov. 05, 2013	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Increase in goodwill		$ 1,894,794	$ 1,656,374	$ 92,789	$ 0
Measurement period adjustments		22,288
CapLease [Member]
Business Acquisition [Line Items]
Estimated fair value of assets	$ 2,036,640
Below-market lease liability	57,058
Decrease to mortgage notes payable		(27,300)
Increase in goodwill	$ 65,450
Measurement period adjustments		$ 27,300
Common Stock [Member] | CapLease [Member]
Business Acquisition [Line Items]
Class of warrant or right, value received by each warrant of right (in dollars per share)	$ 8.50
Preferred Stock [Member] | CapLease [Member]
Business Acquisition [Line Items]
Class of warrant or right, value received by each warrant of right (in dollars per share)	25
Member Units [Member] | CapLease [Member]
Business Acquisition [Line Items]
Class of warrant or right, value received by each warrant of right (in dollars per share)	8.50
Consideration transferred, amount per share (in dollars per share)	$ 8.50
Cash paid for acquired real estate investments	$ 920,697