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Soft Dollar Arrangements - Additional Information (Detail)

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Soft Dollar Arrangements - Additional Information (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Soft Dollar Arrangements [Abstract]        
Soft dollar credits $ 235 $ 263 $ 470 $ 527