Nature of Business and Financial Statement Presentation - Non-cash Investing and Financing Activities (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accounts payable related to construction in progress	$ 20,800	$ 46,300
Dividends declared	75,078	67,900	$ 68,604
Mortgages assumed from acquisitions	0	33,700
Elimination of a previously held equity interest	$ 0	$ 1,400