Stock-Based Compensation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Capitalized stock-based compensation	$ (714)	[1]	$ (557)	[1]	$ (1,410)	$ (948)
Stock-based compensation, net of capitalization	2,262		3,135		4,534	6,159
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	2,915		3,622		5,831	6,978
Shares granted					256,941
Weighted average grant date fair value (in dollars per share)					$ 48.14
Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 61	[2]	$ 70	[2]	$ 113	$ 129

[1] Includes compensation expense specifically identifiable to development and leasing activities.

[2] Includes amortization of the grant date fair value of restricted stock awards over the respective vesting periods.