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Summary of Restricted Stock Award Activity (Detail) (Restricted stock, USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Restricted stock
     
Number of Share Unit Awards      
Beginning balance 551,974 453,575 226,703
Granted 414,076 334,485 411,130
Released (238,498) (181,599) (110,485)
Forfeited (96,085) (54,487) (73,773)
Ending balance 631,467 551,974 453,575
Weighted Average Grant Date Fair Value      
Beginning balance $ 6.90 $ 7.67 $ 6.40
Granted $ 6.32 $ 5.73 $ 8.60
Released $ 6.61 $ 6.51 $ 9.31
Forfeited $ 6.44 $ 7.44 $ 6.49
Ending balance $ 6.70 $ 6.90 $ 7.67