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Stock Buy Back Plans - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2013
Dec. 31, 2012
Nov. 30, 2012
Class A Common Stock [Member]
Dec. 31, 2013
Class A Common Stock [Member]
Dec. 31, 2012
Class A Common Stock [Member]
Dec. 31, 2013
Employee Restricted Stock Plan [Member]
Class A Common Stock [Member]
Dec. 31, 2012
Employee Restricted Stock Plan [Member]
Class A Common Stock [Member]
Class of Stock [Line Items]                      
Stock repurchase program, authorized amount             $ 25,000,000        
Purchase of treasury shares (in shares) 351,313       26,593 377,906     377,906 347,592 75,995 55,463
Purchase of treasury shares         $ 13,791,000 $ 11,208,000       $ 2,600,000 $ 1,800,000