Assets for Reportable Segment (Detail) - Parent Company [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 11,417,376	$ 11,491,919
Same Store [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	9,773,940	9,864,321
Non-Same Store and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	1,439,424	1,427,778
Corporate assets
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 204,012	$ 199,820