Assets for Reportable Segment (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 2,775,008	$ 2,751,068
Large Market Same Store
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	1,279,957	1,108,827
Secondary Market Same Store
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	812,641	654,315
Non-Same Store and Other
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	643,028	949,398
Corporate assets
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 39,382	$ 38,528