Acquisitions and Dispositions - Summary of Business Acquisition Pro-forma Information as Results of Operations (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended
Apr. 30, 2013	Jun. 30, 2013	Jun. 30, 2013
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Accretion (or amortization) of fair market value adjustments		$ 5,599	$ 6,818
Bargain purchase gain	10,044	10,044	10,044
Merger/restructure related costs		(2,479)	(2,479)
Centennial [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Merger/restructure related costs		$ (1,000)	$ (1,000)

In a business combination in which the amount of net identifiable assets acquired and liabilities assumed exceeds the aggregate consideration transferred or to be transferred (as defined), this element represents the amount of gain recognized by the entity.

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

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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