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Goodwill - Narrative (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2012
Mar. 31, 2013
Dec. 31, 2012
Dec. 31, 2012
Merganser
Goodwill [Line Items]        
Goodwill   $ 55,417 $ 55,417 [1]  
Earn out payment $ 13,387     $ 13,387
[1] Derived from the audited consolidated financial statements at December 31, 2012.