Income Taxes (Schedule of Reconciliation of Income Tax Provision (Benefit)) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Computed tax expense	$ 20,791	$ 15,544	$ 15,705
REIT income not subject to federal income tax	(5,241)	(11,739)	(9,481)
State net operating loss and tax credit valuation allowances	0	897	286
State and local taxes, net of federal income tax	1,615	54	311
Adjustment of REIT deferred taxes	0	0	(2,100)
Deferred tax adjustment - Retiree Health Care Act	0	0	1,441
All other items	(356)	(611)	(1,566)
Income Tax Provision, Total	$ 16,809	$ 4,145	$ 4,596
Effective Tax Rate	28.30%	9.30%	10.20%