Summary of Significant Accounting Policies - Revenue Recognition (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Straight Line Rent Adjustments	$ 25.1	$ 20.8

Amount of the adjustment to rental revenues to measure escalating leasing revenues on a straight line basis.

No definition available.

Name:	us-gaap_StraightLineRentAdjustments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration