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Common and Common Equivalent Shares - Schedule of Calculation of Shares Used in Basic and Diluted Net Income Per Share (Detail)
In Thousands, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Weighted Average Number Of Shares Outstanding Reconciliation [Line Items]                      
Weighted average number of common shares outstanding 49,113 [1] 48,938 [1] 48,543 [1] 48,269 [1] 48,126 [1] 47,990 [1] 47,531 [1] 47,149 [1] 48,693 47,706 46,630
Weighted average number of dilutive common share equivalents                 998 1,090 940
Weighted average number of common and common equivalent shares outstanding 50,106 [1] 49,809 [1] 49,545 [1] 49,399 [1] 49,132 [1] 48,935 [1] 48,730 [1] 48,361 [1] 49,691 48,796 47,570
Antidilutive securities not included in the diluted earnings per share calculation                 29 45 464
[1] Basic and diluted per share amounts are computed for each of the periods presented. Accordingly, the sum of the quarterly per share amounts may not agree with the full year amount.