Basis of Presentation - Additional Information (Detail)	Dec. 31, 2012	Dec. 31, 2011
Basis Of Presentation [Line Items]
Ownership interest of sole general partner	95.50%	94.30%
Ownership interest of limited partners	4.50%	5.70%

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

No definition available.

Name:	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant