Carrying Amount and Fair Value of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities		$ 28,235
Secured notes payable	1,044,682	912,067
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities		28,235
Secured notes payable	1,044,682	912,067
Deferred compensation liability	637	520
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities		28,235
Secured notes payable	1,116,162	941,582
Deferred compensation liability	$ 637	$ 520