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Debt - Additional Information (Detail) (USD $)
9 Months Ended
Sep. 30, 2014
Dec. 31, 2013
Jul. 10, 2014
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]      
Revolving credit agreement     $ 125,000,000
Credit agreement expire period, start period Sep. 20, 2017    
Credit agreement expire period, end period Jul. 10, 2019    
Letters of Credit Outstanding 2,977,000    
Debt Outstanding 0    
Unused Revolving credit 122,023,000    
Unrestricted retained earnings $ 92,459,000 $ 148,467,000