Assets for Reportable Segment (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 2,599,088	$ 2,530,468
Large Market Same Store
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	1,125,282	1,017,015
Secondary Market Same Store
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	664,165	668,109
Non-Same Store and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	755,800	760,132
Corporate assets
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 53,841	$ 85,212