Acquisitions and Dispositions Acquisitions (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Allegheny County Airport – Allegheny County Airport [Member]
Business Acquisition [Line Items]
Bonus Payment in Escrow	7.60%
Bonus Payment	$ 46,315
Allegheny County Airport – Pittsburgh International Airport [Member] [Member]
Business Acquisition [Line Items]
Gas and Oil Area, Undeveloped, Gross	9,263

Lease area in which a working interest is owned and on which wells have not been drilled or completed to a point that would permit the production of commercial quantities of oil and gas regardless of whether or not such area contains proved reserves.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Industry Guide

-Number 2

-Paragraph 5

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Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant