Tenant and Other Receivables: (Details) (USD $) In Thousands, unless otherwise specified							12 Months Ended			0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Accrued percentage rents	Dec. 31, 2011 Accrued percentage rents	Dec. 31, 2012 Note receivable secured by deed of trust	Dec. 31, 2011 Note receivable secured by deed of trust	Dec. 31, 2012 Note receivable from Pederson	Dec. 31, 2011 Note receivable from Pederson	Dec. 31, 2010 Note receivable from Pederson	Mar. 27, 2012 Note receivable from AWE Talisman Company item
Tenant and Other Receivables:
Allowance for doubtful accounts	$ 2,374	$ 4,626
Components of tenant and other receivables, net
Accounts receivable			9,168	7,583
Deferred rent receivable due to straight-line rent adjustments	49,129	47,343
Note receivable, interest rate (as a percent)					5.50%		11.60%			5.00%
Notes receivable					8,502	8,743	3,445	3,445		12,500
Number of notes receivable										2
Interest income on notes receivable							$ 518	$ 413	$ 138	$ 478